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Access to a sufficient quantity of safe water is widely recognized as fundamental to ensure health and prevent water- and excreta-related diseases. The objective of this study is to analyze seasona...

Droplet manipulation plays an important role in scientific research, daily life, and practical production such as biological and chemical analysis. Inspired by the structure and function of three typical leaf veins, the bionic texture was replicated by the template method, and the artificial leaf was selectively treated by nanoparticles to obtain a quasi-three-dimensional hybrid superhydrophobic-hydrophilic surface. When the droplet touches the surface of the leaf, it will be attracted to the bottom of the main vein from different directions even in horizontal conditions due to the Laplace pressure gradient and energy gradient. The simulation analysis demonstrates that the reason for directional transportation is the energy gradient of the droplets on the different levels of veins, including the thin veins, lateral veins, and main vein. Meanwhile, the experimental result of water collection also showed an outstanding directional transportation effect and excellent water collection efficiency. In addition, when the sample is tilted upside down, the droplet will flow back to the main vein along the lateral vein and then flow down the main vein, showing a good droplet pumping effect. Therefore, the directional and polydirectional transportation of droplets on the same sample is successfully realized, and the conversion between executing single and multiple tasks simultaneously can be realized only by upright and inverted samples. This work provided a new strategy for directional and polydirectional water manipulation, water collection, directional drainage, and microfluidic devices.

Efficient water harvesting from vapor has attracted increasing attention in recent years owing to its potential to address the daunting water crisis. However, a fundamental challenge limiting the water collection efficiency from vapor is the intrinsic trade-off between fast droplet nucleation and efficient droplet removal, both of which have distinctively opposite requirements in surface chemistry and morphology. Inspired by the elegant topography features and functions of desert beetles and cactus thorns, herein, we designed a novel hybrid wetting surface consisting of wedge-shaped patterns, in which the patterns mimic the bumpy back of the desert beetle for enhanced water nucleation, whereas the wedge-shaped topography renders unconventional oblique droplet jumping and long-range transport. The synergistic cooperation of these two effects effectively decouples the inherent trade-off, leading to more than an 11 times increase in water harvesting compared to that of a superhydrophobic surface. Thus, our findings have extensive applications in water harvesting, power generation and desalination.

Inspired by nature, Janus membranes with unidirectional liquid transport (ULT) were developed to be used in the fields of fog collection, moisture-wicking fabrics, demulsification, etc. However, the obtained Janus membranes are often unifunctional, and it is still a great challenge to adjust the ULT of Janus membranes for multifunctional applications. Herein, a scalable, low-cost, and machine-washable Janus membrane was developed by combining the cyclic self-assembly of phytic acid and FeIII and a one-side spraying coating of poly(dimethylsiloxane) (PDMS), featuring adjustable ULT upon challenge for multifunctional applications. By controlling the amount of PDMS, the Janus membranes exhibit two different performances, ULT and switchable permeation. The prepared Janus membranes achieved an excellent moisture-wicking fabric (1.6× the water evaporation rate of cotton), fast water collection under oil, rapid demulsification, and the efficient separation of an oil/water mixture. The separation efficiency of a light or heavy oil from water was higher than 99.9% even after 10 separation cycles, and the flux of the separation was up to 2.55 × 104 or 2.38 × 104 L m-2 h-1, respectively. This study could provide an idea for the development of more Janus membranes with adjustable performances to realize multifunctional applications.

Development of porous materials with anti-fouling and remote controllability is highly desired for oil-water separation application yet still challenging. Herein, to address this challenge, a sponge with unusual superhydrophilicity/superoleophobicity and magnetic property was fabricated through a dip-coating process. To exploit its superhydrophilic/superoleophobic property, the obtained sponge was used as a reusable water sorbent scaffold to collect water from bulk oils without absorbing any oil. Owing to its magnetic property, the sponge was manipulated remotely by a magnet without touching it directly during the whole water collection process, which could potentially lower the cost of the water collection process. Apart from acting as a water-absorbing material, the sponge can also be used as affiliation material to separate water from oil-water mixture and oil in water emulsion selectively, when fixed into a cone funnel. This research provides a key addition to the field of oil-water separation materials.

An anomalous layer enriched with chemical elements indicating the presence of terrigenous matter was discovered in the sediment core of Zapovednoe Lake located 60 km from the epicenter of the Tunguska event (1908) using synchrotron radiation X-ray fluorescence spectroscopy (SR–XRF). Radioisotope measurements indicate that the age of the layer is consistent with the date of the catastrophe. Apparently, the anomalous layer was formed as a result of an intense terrigenous matter inflow from the water catchment area due to massive forest falls and subsequent wildfires caused by the Tunguska event. Thus, it is established that targeted searches for microparticles of extraterrestrial origin can be carried out in the discovered and dated anomalous bottom sediment layer.

Water collection time is a key indicator in tracking access to drinking water. Over the years, water surveillance agencies have relied on water collectors for information on water collection time to measure progress of water supply. However, emerging evidence shows that water collection times reported by water collectors in developing countries are often imprecise. To contribute to knowledge about the validity or otherwise of self-reported water collection times, this study explored the association between self-reported water collection times and observed water collection times in the Upper West Region of Ghana. Data on water collection times were gathered from 412 water collectors in Daffiama-Issa-Bussie District and Lawra Municipality, first through interviews, and second by observation. From the results, self-reported water collection times were significantly (P < 0.01) lower than observed water collection times. The average round-trip water collection time reported by water collectors (32 minutes) was 8 minutes lower than observed water collection times (40 minutes). This implies that existing statistics on basic water coverage that are largely based on self-reported water collection times are overestimated. Going forward, we call on water surveillance agencies to collect data on water collection times through observation. This article has been made Open Access thanks to the generous support of a global network of libraries as part of the Knowledge Unlatched Select initiative.

A hydrological model was applied to select the best infilling method of missing precipitation (1) and to assess the impact of the length of deleted and filled precipitation data (2). The model was calibrated and validated using the hourly observed discharges from two gauges located in the outlet of the catchment (62.34 km2) and in the inner sub-catchment (2.05 km2). Precipitation from four gauges was spatially interpolated over the overall catchment, while the sub-catchment used the precipitation from one gauge. Four scenarios of different lengths of deletion within three high-intensity events were established in the data of this gauge. Three infilling methods were applied and compared: substitution, linear regression and inverse distance weighting (IDW). Substitution showed the best results, followed by linear regression and IDW in both scales. Differences between methods were significant only in 8.3% and 19.4% of all cases (sub-catchment and catchment, respectively). The impact of length was assessed using the substitution only and by comparing differences in discharges and performance statistics caused by four scenarios. Higher differences in discharges were found on the catchment scale compared to the inner sub-catchment and were insignificant for all events and scenarios. The hypothesis that a longer length of deleted and filled data would lead to a greater error in discharges was wrong for 11.1% and 16.7% of all cases (sub-catchment and catchment, respectively). In several cases (33.4% sub-catchment, 27.1% catchment), the model produced better results using the time series with filled gaps compared to the configuration with observed data.

In arid deserts, water supply is supplemented by water from fog and condensation. Once the droplets are collected, they are transported to a location where they are consumed or stored before they evaporate. Conical geometries or triangular patterns are known to create Laplace pressure gradient inside droplets which facilitates droplet transport. Water collection by fog on conical and triangular patterns have been studied. The research on the water collection by condensation exist only on flat triangular patterns. These flat surfaces have limitations for practical purposes, such as the Laplace pressure gradient does not act of droplets unless they touch the border. That is not the case in cones, which makes them superior for practical water collection. In this study, for the first time, water collection from condensation on cones have been studied. Cones of different tip angle, cone length, and surface area were used. Effect of inclination angle and array was also characterized. The results are compared to water collection by fog.

The growing concerns over desertification have spurred research into technologies aimed at acquiring water from nontraditional sources such as dew, fog, and water vapor. Some of the most promising developments have focused on improving designs to collect water from fog. However, the absence of a shared framework to predict, measure, and compare the water collection efficiencies of new prototypes is becoming a major obstacle to progress in the field. We address this problem by providing a general theory to design efficient fog collectors as well as a concrete experimental protocol to furnish our theory with all the necessary parameters to quantify the effective water collection efficiency. We show in particular that multilayer collectors are required for high fog collection efficiency and that all efficient designs are found within a narrow range of mesh porosity. We support our conclusions with measurements on simple multilayer harp collectors.

Vapor condensation and condensate collection play a crucial role in solar water desalination, which is a promising solution to the shortage of freshwater. However, the currently used condensers based on thermal conduction and/or convection cooling are limited in cooling power for vapor condensation, whilst their surface wettability requires appropriate modulation to facilitate condensate collection. In this work, we achieve efficient water collection via using a wettability and spectral selectivity engineered coating comprising hydrophobic SiO2 and hydrophilic TiO2 nanospheres at an optimized weight ratio. The tuning of surface wettability promotes a dropwise collection mode, leading to maximized droplet harvesting performance of 1047 mg·cm−2·h−1. Further, the coating can spontaneously cool itself by reflecting ~90% of the incident sunlight whilst emitting >95% of thermal infrared rays, leads to a daytime sub-ambient temperature drop of 7 °C. Hence, under an ultra-humid condition that mimics a solar water-purification system, the coating that integrates daytime radiative cooling with dropwise collection demonstrates an excellent water production rate, which is superior to those of the hydrophilic surface and the surface with restricted radiative cooling access to the sky. Moreover, the coating comprising TiO2 photocatalyst can recover its wettability through the photocatalytic degradation of adsorbed oily dirt pollutants.

This study was conducted in the Caiman forest on Mahe in the Seychelles – an important water catchment area that suffers from different land use activities and also from invasive species. The aim o...

The objective of this research was to investigate the current status of water-collection behaviours and their determinants, which are associated with the burden of collecting water. This research was focused on the remote hinterlands of Nepal, and little is known about the residents’ livelihoods; therefore, particular attention was paid to the household burdens in terms of the time devoted to water-collection activities. A survey was conducted in households from mountainous regions of Nepal whose infrastructure is limited in terms of poor water supply and access to electricity. The results of the survey indicated that one or two members of a household were responsible for collecting water, and approximately 40% of households used multiple sites. Moreover, household members visited their collection location approximately 3–4 times per day. Based on the water-collection behaviours of each household member, an average of 148.6 min were used for water-collection activities each day. The factors associated with the total time devoted to water-collection activities include the number of household members, the sex of the household head, the number of years of education of the household members, and the share of children and women engaged in water collection. The estimation results also indicated that members of households with access to water storage spent less time collecting water. The results yield key information from villagers in remote mountainous regions, and substantial improvement is pivotal for achieving universal water access under sustainable development goals.

Creation of methods for complete and cost-effective collection of water droplets from an aerosols arising as a by-product of the low-potential heat uptake from industrial equipment is one of the key tasks of rational use of water resources contributing to the improvement of the environment near large industrial enterprises. This paper shows how the application of materials with extreme wettability and a specific surface topography in spray separators can significantly increase the water collection efficiency.

Inhabitants of the upper Himalayan regions entertain a belief that the Chir Pine trees are ingressing the Broadleaf forest areas and that these areas are gradually turning into water stressed regions as Chir Pines adversely influence water recharge and water availability. This paper examines whether and to what extent the Chir Pine forest areas are water stressed compared to Broadleaf forest areas by studying the household coping cost in relation to water stress. We use the coping cost differences thereafter to value the relative water provisioning services of forest types. We conduct multiple focus group discussions, a questionnaire survey and statistical analyses to derive the results. Results show all households, except the ones living near Deodar forest, to face water stress in summer but the Chir Pine areas are the most water-stressed. Both comparison of mean and multivariate regressions of water collection time and other coping costs show that the villagers surrounded by Deodar, Deodar mix pine, Broadleaf mix bush or Broadleaf mix pine forests spend much less time for water collection and spend less on water treatment and storage compared to the villagers surrounded by Chir Pine forest irrespective of elevation, aspect or model used. These differences in water collection time amount to a wage income loss between USD 31 and USD 318 in India, and between USD 23 and USD 238 in Nepal per year per household, in Chir Pine areas compared to other forest areas.

Inspired by the Stenocara beetle that can collect water from moist air in the Namib desert, here, we propose a simple dynamic control of crystal growth of ZIF on a natural polymer, soy protein. By adjusting the precursor concentration as well as the crystal growth time, hierarchical micro-/nano-crystals are constructed on the protein film surface. Taking advantage of the size difference of such crystals, selectively hydrophobic modification with a low surface-energy agent, stearic acid, can be performed on the surface, creating controllably hydrophilic/superhydrophobic patterns in favor of efficient water harvesting from fog. The effects of the as-prepared patterns on the water condensation behavior and collection efficiency are investigated; the maximum water collection efficiency, notably, can reach as high as 917.6 mg·cm−2·h−1. The results suggest that the biomimetic films hold a potential application in atmospheric water collection and the simple pattern-constructing approach is helpful to develop functional surface-patterned materials.

Acute water security vulnerability at regional to local scales is becoming increasingly apparent. In 2017, officials in Cape Town, South Africa, designated the term “Day Zero” to demark an exact time when the city’s taps would be switched off due to critically low reservoir levels. Beyond Day Zero, residents would need to converge at communal water collection points to access a 25-L daily ration of water. The particulars of the crisis and stakeholder responses prove informative to other cities.

Nature-inspired water collection technology has been well-recognized as an effective solution for relieving water shortage hardships, and yet remains challenging when being used in an actual natural environment. In this work, we have successfully developed a promising water-collecting windmill that can be used in complex windy environments, by taking integrative inspiration from the liquid-manipulation strategies adopted by rice leaves, cacti, Nepenthes pitcher plants, and butterflies. The unique directional grooves on the blade surface with ridge-like walls with a shape gradient, combined with a molecular slippery layer, are crucial for not only water deposition but also directional drainage in water collection. Besides, the engineering design of rotatable blades turns the adverse effect of strong winds into a positive one, along with the nature-inspired surface topography and physicochemical property. Such a novel windmill has shown unprecedented water-collecting performance in a static environment, in strong wind, and in intermittent wind. Furthermore, the windmill can sense the wind-blowing direction and adjust its facing direction accordingly to ensure maximum utilization of wind power. It is believed that this work will bring a broad guiding significance to the design of smart water-harvesting materials and devices for application in more complex situations.

Summary In this paper we describe a novel method for water unloading of natural gas wells in mature reservoirs experiencing low reservoir pressures. Current methods for water unloading from gas wells have at least one of the drawbacks of restricting gas production, requiring external energy, using consumable surfactants, or being labor intensive. The proposed design offers a new approach to water unloading that does not restrict or interrupt gas production. It can operate without external energy, and uses no consumables. Virtual and physical simulators have been developed and the full-scale version of the concept has been studied in test wells to demonstrate the feasibility and performance of the new water-unloading concept. An industrial-grade preproduction prototype was tested successfully in a test gas well to validate this study.

Water is essential in educational buildings as it serves several purposes, such as: drinking, cleaning, and construction work. Therefore, it is necessary to rationalize its consumption for its importance, as it is the core of the current water wealth and it is one of the most controversial issues in achieving the concept of sustainability. Egypt is facing a lot of problems and pressure on water supplies. Adopting water sustainability in schools is basically focused on reducing consumption, water collection, and water recycling. The paper tackles and highlights the sustainable methods, technique, and initiatives that are implemented in the internal and external design of school buildings, how to manage sustainable water in schools, in addition to an access to guidelines and recommendations on future proceedings for more sustainable schools. This research aims to provide easy-to-read guideline to facilitate the management of sustainable water in schools. It includes guidance on the application of sustainable water utilization and sustainable drainage, during the stages of school design and operation. The study discusses sustainable water management in some of the global schools in various areas of the world, where these schools have successfully adopted water efficiency and preservation standards and applied the criteria and measures of sustainability. Keywords: Sustainable water management, Sustainable school, Greywater, Rainwater, Guidelines

A novel integrative bioinspired surface with wettable patterns and gradient (WPGS) is proposed for fog collection via a novel anodic oxidation strategy. We study the water collection behaviors on WPGS with different parameters. Quantitative force analysis is presented, providing evidence for the underlying mechanism leading to the directional motion of the droplet, which is consistent with the experimental results. Such a surface can not only improve the fog droplet capture performance effectively owing to wettable patterns but also accelerate surface regeneration by taking full advantage of the cooperation of multidriving forces, leading to a further fog collection enhancement.

Surface functionalization has important application prospects in many aspects, for example, anti-drag, anti-pollution, anti-icing, self-cleaning, reversible adhesion, water collection, and so forth...

Rainwater harvesting on buildings is directly related with water collection surfaces and thus with the building form. In this study, the amount of rainwater obtained using different building forms in different climatic regions were analysed comparatively. Two scenarios were used in this study. In the first scenario, 2 different public housing developments with different building forms and roof styles but with same occupant numbers and same site area in Bursa in the temperate-humid climate region and Diyarbakir in the hot-dry climate region were evaluated in relation to rainwater collection and water conservation. In the second scenario, a typical project developed by TOKI for the temperate climate region was also applied to the hot-dry climatic region and the amount of collected rainwater was evaluated taking into account also the characteristics of climatic region. The study found that in the first scenario 18% and 7%, and in the second scenario 13% and 5% of annual water consumption only in toilet flushing and bathrooms respectively (toilet flushing, sinks and bathtubs) was met by collected rainwater in Development 1. These values were 34% and 13% respectively for Development 2.

Water scarcity plagues two-thirds of the global population. Interestingly, researchers have found that spider silk exhibits excellent water-collection ability owing to its unique structure and chemical components. Based on this characteristic, numerous bioinspired fibers have been fabricated for water collection. Herein, we review the water-collection process for spider silk and recent vital advances in bioinspired fibriform materials, focusing on the water-collection mechanisms of spindle-knot fibers, which exhibit directional droplet transport, hanging mechanism and hanging ability. Also, we evaluated their water-collection abilities on a micro- and macro-scale, which gave a better view for the design of bioinspired water-collection materials. These advances enable the significant use of bioinspired fibers in water collection, which may be applied in several other fields, such as directional transport, tissue engineering, oil-water separation and biosensors.

Freshwater shortage has been receiving considerable attention, and water harvesting is one of the potential solutions to this water crisis. Several researchers have tried to improve the harvesting capabilities by changing mesh wettability for atmospheric fog harvesting. However, the wettability effect on water harvesting from white plumes has not yet been investigated thoroughly, despite industrial cooling towers being considered as alternative water resources, because of the large amounts of fog plumes generated. In this study, surface wettability was modified with a robust and simple method for practical scaled-up applications, and we explored the influence of mesh wettability on atmospheric and industrial fog harvesting. In atmospheric fog harvesting, both superhydrophilic meshes (SHPMs), and superhydrophobic meshes (SHBMs) were found to improve the harvesting performance, with superhydrophobic treatments providing the best collection efficiency. In contrast, only superhydrophilicity improves the performance in industrial fog harvesting with flat mesh screens. We hypothesize that this research will be useful for mesh design, as it analyzes the influence of mesh wettability on the performance of water collection in both atmospheric and industrial water harvesting.

Our knowledge on spider silks shows the importance of joining heterogeneous structures and surface chemical compositions in preparing fibers, fibrous surfaces, and 3D materials with a controllable wettability. We start our review with spider silk and proceed to the historical development of nature-inspired spinning processes, their products, and their advantages and disadvantages. Relevant wetting states are then summarized in fiber-based systems. Recent applications are reviewed, including one-dimensional spindle-knotted fibers for highly efficient fog harvesting, long-distance transport, and stimulus-responsive wettability and two-dimensional spindle-knotted fibrous systems for water collection, functional surfaces, and filtration. Finally, we offer some perspective on future research trends regarding biomimetic fibers for wetting-controlled engineering.

At present, collecting water directly from the atmosphere has become an effective means to solve the growing shortage of fresh water. Inspired by the structures of trichomes (hairs) of Sarracenia to capture fog and transport water, a series of different high-low rib-like hierarchical texture surfaces were prepared based on the laser method. These surfaces have gradient superwetting and adhesion because of the differences in subsequent preparation methods. In addition, this work discusses the effect of the above performance differences on the efficiency of fog collection and the surface condensation characteristics during fog collection. The results show that the surface of the laser-prepared sample with the mixing unit combination has more efficient fog collection efficiency and droplet removal rate. After 30 min, the amount of drip measured in the atmospheric environment is 8.4 times that of the polished surface. This indicates that the multihierarchical textured surface and superhydrophobicity are essential for improving the droplet removal rate and coagulation efficiency.

The delimitation of sampling points is an important step to avoid unnecessary costs in water collection process and laboratory analysis. Based on the accumulated reflectance of PlanetScope imagens, it was possible to verify areas of greater spectral variability related to the presence of Optically Active Components (OAC). In order to do that, the accumulated reflectance method was used, based on multitemporal images. For that, three PlanetScope Ortho Scene Products were tested: Atmospheric Corrected for Surface Reflectance (SR), Digital Number (DN), and Top of Atmosphere Reflectance (TOA) images. SR and DN products had similar outcome, while DN product was not ideal for the purpose of this article. Even though SR and DN products were able to delimitate sampling points, they may have radiometric issues, mainly because of their near infrared values.

Directional transport of water droplet on curved track attracts considerable research interest in microfluidics. In this work, we first study the directional transport of water droplet on super-hydrophilic curved track. The water droplet can quickly move along the whole super-hydrophilic track without deviation. The speed of the water droplet on the super-hydrophilic track is 0.075 m/s. In theory, the van der Waals’ force existing in the super-hydrophilic track keeps the water droplet from deviating during rapid movement. In addition, we further study the influence of track geometry and water droplet size on the transport capacity of the super-hydrophilic track. Compared with track depth, the track width has a great effect. The water droplet deviates from the track with a width of 50 μm. But the water droplet can directionally move along the super-hydrophilic track with a width of 100 μm and 150 μm without deviation. In addition, for the same super-hydrophilic track, the larger the water droplet volume, the easier it is to deviate from the track. Finally, to demonstrate the application of super-hydrophilic track on superhydrophobic surface, we performed the rapid mixing and directional collection of water droplets. This strategy is of great significance for extending it to applications such as microchannels in microfluidics, water collection systems, and others.

Lack of access to safe drinking water on premises remains widespread in low- and middle-income countries. Interventions to improve access to safe water at the point of collection are essential, but water safety at the point of consumption is also an important consideration. This research aimed to 1) improve understanding of household practices in collecting water with respect to seasonality, and 2) to further assess risk associated with post-collection contamination from the point of collection to the point of consumption. A seasonal cohort study, including 115 households, was conducted in Malawi. Along with household surveys and observations, samples of water were tested for microbial water quality at four different stages of water collection: water source, collection container, storage container, cup of drinking water. Using E. coli as an indicator of contamination (cfu/100 ml), the risk of post-collection contamination was assessed. The results indicate that most water sources were free from contamination; contamination was proportionally lower in the dry season when more sources were found to be classified as having a very low risk of contamination. However, the level of risk of contamination was more likely to increase following collection in water sources that were initially free from contamination. Results show that the degradation in water quality from the point of collection to the point of consumption was more important in the rainy season, which is likely to be driven by the effect of seasonality on the household environment. Filling the collection container at the point of collection and storage at the point of consumption were found to be critical stages for an increased risk of E. coli contamination. Understanding household practices in accessing and handling water during both rainy and dry season is necessary to target appropriate interventions to reduce post-collection contamination.

Biological creatures with unique surface wettability have long served as a source of inspiration for scientists and engineers. More specifically, certain beetle species in the Namib Desert have evolved to collect water from fog on their backs by way of wettability patterns, which attracted an ongoing interest in biomimetic studies. Bioinspired materials exhibiting extreme wetting properties, such as superhydrophilic and superhydrophobic surfaces, have attracted considerable attention because of their potential use in various applications. Combining these two extreme states of superhydrophilicity and superhydrophobicity on the same surface in precise two-dimensional micropatterns opens exciting new functionalities and possibilities for a wide variety of applications. In this review we briefly describe the water-harvesting mechanisms of a genus of Namib Desert beetle, Stenocarpa, consisting of the theory of wetting and transporting. Then we describe the methods for fabricating superhydrophilic-superhydrophobic patterns and highlight some of the newer and emerging applications of these patterned substrates that are currently being explored. Finally, we provide conclusions and outlook concerning the future development of bioinspired surfaces of patterned wettability.

International audience; The purpose of this article is to investigate the storing behaviours in the South of France in the late Neolithic period, in plateaus and lowland structures. Plateaus are limestone formations that present multiple natural cavities for the Neolithic people to use, but in return, have no surface water to offer. The subterranean nature of water has profoundly shaped the storing behaviours in the plateaus as it is mostly turned towards water collection and storage. In the lowland area however, substructures were dug directly in the soil and ceramics were used aswell as possible organic containers. This paper aims to address the similarities and differences between the usage of caves and cellars. The application of a use-wear analysis on ceramic vessels brings new insights on past food practices.

Fangzhu, which has been lost for thousands of years, is an ancient device for water collection from air, its mechanism is unknown yet. Here we elucidate its possible surface-geometric and related physical properties by the oldest the Yin-Yang contradiction. In view of modern nanotechnology, we reveal that Fangzhu’s water-harvesting ability is obtained through a hydrophilic-hydrophobic hierarchy of the surface, mimicking spider web’s water collection, lotus or desert beetle’s water intake. The convex-concave hierarchy of Fangzhu’s textured surface enables it to have low wettability(high geometric potential) to attract water molecules from air through the nano-scale convex surface and transfer the attracted water along the concave surface to the collector. A mathematical model is established to reveal three main factors affecting its effectiveness, i.e., the air velocity, the surface temperature and surface structure. The lost technology can play an extremely important role in modern architecture, ocean engineering, transportation and others to catch water from air for everyday use.

Issues surrounding water infrastructure, access, and quality are well documented in the Central Appalachian region of the United States. Even in cases where residents have in-home piped point-of-use (POU) water, some rely on alternative drinking water sources for daily needs&mdash, including water collection from roadside springs. This effort aims to better understand and document spring usage in this region by identifying the factors that influence drinking water source selection and comparing household and spring water quality to Safe Drinking Water Act (SDWA) health-based and aesthetic contaminant recommendations. Households were recruited from communities surrounding known springs in three states (Kentucky, Virginia, and West Virginia). First- and second-draw, in-home POU tap water samples were collected from participating households and compared to samples collected from local springs on the same day. Samples were analyzed for fecal indicator bacteria and inorganic ions. Study participants completed surveys to document perceptions of household drinking water and typical usage. The majority of survey participants (82.6%) did not trust their home tap water due to aesthetic issues. Water quality results suggested that fecal indicator bacteria were more common in spring water, while several metallic ions were recovered in higher concentrations from household samples. These observations highlight that health risks and perceptions may be different between sources.

Inspired by both the water collection strategy of desert beetles and the lubrication effect of Nepenthes pitcher plants, a new flexible functional surface for water collection is designed and can be easily fabricated. Such a functional surface consists mainly of a superhydrophobic region and a hydrophobic region with infused lubricating oil. Different functional patterns can be easily manipulated by different templates. Due to the flexibility of the surface, not only a two-dimensional surface but also a three-dimensional one can be designed. Directional water collection can be achieved. Furthermore, it is an integrative bioinspired functional surface that does not require any tailoring. Compared with existing functional surfaces, the present surface has higher water collection efficiency in fog and such a function can last 15 days. The functional degraded surfaces can also be easily reused.

Inspired by Nepenthes pitcher plants, slippery liquid-infused porous surfaces (SLIPS) have recently attracted increasing attention for directional transport and movement manipulation of water droplets. Nevertheless, infused lubricants are generally instable and easy to deviate from such surfaces during applications, resulting in the lost control on the fog capture and motion of droplets as well as serious risk of water safety. Here, a highly stable SLIPS with improved lubricant storage is developed through the structure design of synergistically constructing regular micro-pincushion and nanoparticles. Notably, on the basis of the microstructure, the presence of nano-architecture shows great contribution to obviously increased capillary force as well as suppressed lubricant loss during water collection. Featuring the stable surface-slippery property, the biomimetic SLIPS displays well maintained dropwise coalescence of water from fog and efficient water harvesting performance. The water collection efficiency is as high as 852 mg cm-2 h-1 and is stable within continuous 20 h application. This fundamental illustration of structural synergism can be further applied to construct more new water manipulation and harvesting platforms with stably slippery surfaces/interfaces.

Fresh water sustains human life and is vital for human health. It is estimated that about 800 million people worldwide lack basic access to drinking water. About 2.2 billion people (nearly one-third of the global population) do not have access to a safe water supply, free of contamination. Also, over 2 billion people live in countries experiencing high water stress. Current supply of fresh water needs to be supplemented to meet future needs. Living nature has evolved species which can survive in the most arid regions of the world by water collection from fog and condensation in the night. Before the collected water evaporates, species have mechanisms to transport water for storage or consumption. These species possess unique chemistry and structures on or within the body for collection and transport of water. In this paper, an overview of arid desert conditions, water sources and plants and animals, lessons from nature for water harvesting, and water harvesting data from fog and condensation are presented. Consumer, emergency and defence applications are discussed and various designs of water harvesting towers and projections for water collection are presented. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 3)’

To address water shortages worldwide, proactive measures are needed to supplement the water supply. In arid regions, many plants and animals use fog or the moisture in air as a source of water. An important consideration for efficient water collection is to transport collected water droplets as rapidly as possible to storage/use before they are evaporated. Triangular geometry has been used for faster transport of water droplets. In the case of a triangular geometry, if a droplet is placed at its apex, the droplet is driven across the triangular region by the Laplace pressure gradient. However, the magnitude of the gradient decreases along the triangle. In this study, nested triangles were designed to provide a higher pressure gradient. Water condensation and transport studies were carried out on the nested pattern at a temperature below the dew point in ambient air. It was found that the nested pattern increases the droplet travel speed. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 3)’.

Oily water treatment has become an urgent need in our daily life because of its harmful potential to the ecological system. In recent years, functional materials with superwetting or superantiwetting property have experienced a rocketing development due to their applications in various areas, including self-cleaning, anti-icing, printing, water collection, liquid transfer, oil/water separation, and so on. In this regard, recent advances in polymer science hold the promise of fine-tuning the composition and morphology for a targeted design to meet the requirements in specific application fields. This review focused on polymeric materials, especially smart polymers, for controllable oil/water separations. Starting from the fundamental theories and criteria related to the separation mechanisms, different stimuli including pH, solvent, ions, chemicals, temperature, photo, electric, pressure, and dual stimuli for triggering smart oil/water separation processes were summarized. Highlights on polymer types, polymer synthesis approaches, separation materials fabrication method, as well as separation performances were present. Current limitations and future perspective were also given. This review aims to offer deep insights into polymer-based interfacial science and provide guidance for the fabrication of smart polymeric surfaces for oily water separation.

Fog water is a valuable resource in places were fresh water is scarce and fog events occur frequently. Fog collectors (FCs) are the technology currently used for harvesting it. In this work we present an electrostatic method for achieving this. A radial electric field is generated between two electrodes which exerts electric forces over the fog droplets that guide them to a collection place. A prototype with a novel design was built and tested on laboratory and field conditions proving that the method works and even outperforms standard FCs with collection rates per unit cross-sectional area about 60% higher.

Water collection from moisture and fog has been of particular interest to arid areas. To mimic the water-collecting capacity of Namib desert beetles, herein, we exploit a facile and low-cost approa...

We present a gas-in-water microfluidic method to precisely fabricate well-controlled versatile microfibers with cavity knots (named cavity-microfiber), like tiny-cavity-microfiber, hybrid-cavity-microfiber, cavity-microfiber, and chained microfiber. The cavity-microfibers are endowed with tunable morphologies, unique surface properties, high specific surface area, assembling ability, flexibility, cytocompatibility, and hydroscopicity. We assemble cavity-microfibers as 3D scaffolds for culturing the human umbilical vein endothelial cells (HUVECs) and dehumidifying. The HUVECs on the scaffolds demonstrate good cell viability and 3D HUVECs frameworks, confirming the unique cytocompatibility of cavity-microfiber. And the cavity-microfibers and their scaffolds also demonstrate excellent dehumidifying ability and large-scale dehumidifying, respectively. Our cavity-microfiber can offer a broad range of applications in sensor, wearable electronics, dehumidifying, water collection engineering, drug delivery, biomaterials, and tissue engineering.

Vertically Aligned Carbon Nanotubes (VACNTs) are well known for their easy production and great modification possibilities, such as oxidation and exfoliation. Some functionalization methods can quickly change carbon nanotubes wettabillity from super-hydrophobic to super-hydrophilic. These last ones have great potential for fog harvesting or other humid gas mixture harvesting. In this work, we used these carbon nanotubes features to develop a super-hydrophobic/super-hydrophilic patterned surface to collect water droplets from humid air. This structure has been designed to biomimic the Stenocara beetle one. In this work we show that water condensation happens on self-cleaning super-hydrophobic surface and then the droplets are pumped by the super-hydrophilic surface. The super-hydrophobic surface was made by deposition of polyethylene on pristine VACNTs/steel screen. The super-hydrophilic surface was fabricated by deposition of functionalized VACNTs on carbon fiber felt. We performed the water collection measurement into a homemade chamber with fog-like humidity control. The best result reached was about 30 (L/m2)/h under controlled conditions.

Hybrid wetting surfaces have been developed to enhance condensation heat transfer, water collection and seawater desalination, due to the advantages of high droplet nucleation efficiency and excellent removal effect. However, there are still many difficulties to overcome before a simple, operable and low-cost system can be exploited in large-scale practical applications. In the present report, an applicable way to fabricate sprayable hybrid wetting coatings mixed with superhydrophobic and hydrophilic particles is described. Conventional condensation tests are carried out for comparison of the nucleation, growth, coalescence and ejection behaviors of dewdrops on a hybrid wetting surface with different hydrophilic particles. Test results showed that a hybrid wetting surface with superhydrophobic and hydrophilic particles has a higher drop number density than a homogeneous superhydrophobic surface has. As expected, this advantage was exhibited also in the water collection test.

Flexible devices that can sustain large deformations have recently attracted widespread interest. In this paper, we investigate several strain-dependent properties of wrinkled Au/PDMS films. We discover a strain-induced hydrophobic to hydrophilic transition on Au/PDMS due to the transition from the Cassie-Baxter-like state to the Wenzel state. We observe that the Au/PDMS also exhibits strain-dependent SERS behaviours and excellent electrical conductivity and stability and can sustain a tensile strain of ∼30% for up to 100 cycles. This method is simple, general and feasible, which may be beneficial for the design and fabrication of flexible units for electronic devices, self-cleaning, microfluidic devices, water collection, and stress monitoring.

Funding of the public water supply in developing countries is often justified by the expectation that it significantly decreases the time spent on water collection, leading to increased labor force participation of women. We empirically test this hypothesis for rural Benin. Daily water collection times are reduced by 41 minutes but still take 2 hours after the installation of a public pump. Even though walking distances are reduced, women still spend a lot of time waiting at the water source, and not all women use the improved water source. Moreover, a reduction in time to fill one water container induces women to fill more containers per day. Time savings are rarely followed by an increase in the labor supply of women. The economic value of the annual time savings is 1%–2% of a rural households’ income.

Bioinspired microfibers for water collection have attracted increasing attention with the aim of alleviating water shortages in water-deficient areas. Here, we review recent progress in microfibers inspired by spider silk for water collection. We summarize and analyze the fiber types, fabrication methods, water-collecting mechanisms and water collection behaviors of bioinspired microfibers and make predictions about future trends in bioinspired microfibers for water collection. This review will be highly beneficial for the design of bioinspired microfibers and increasing their water collection efficiency, even in the fields of fiber-based sensors, oil-water separation, fluid control and smart functional materials.

Namib Desert beetles harvest water from harsh environments by using their hydrophilic-hydrophobic dorsal surfaces. Generally, Cassie-state superhydrophobic materials are chosen as substrates to prepare bioinspired (super)hydrophilic/(super)hydrophobic patterned surfaces. However, due to the low adhesion and strong repellency, aqueous solution cannot be directly set on Cassie superhydrophobic materials until the dropping volume is larger than 6.5 μL. Therefore, arranging a (super)hydrophilic substance on Cassie superhydrophobic substrates to construct (super)hydrophilic/superhydrophobic patterned surfaces still remains a challenge. In this work, by prewetting with dichloromethane (DCM), the mussel-inspired hydrophilic and bio-adhesive dopamine solution (DA) could be dripped onto a Cassie superhydrophobic Cu surface with an ultralow volume of 0.1 μL, whereby low surface tension DCM would "cloak" the high surface tension DA. Along with DCM volatility, DA was adhered on the Cassie superhydrophobic surface and would then self-polymerize into hydrophilic polydopamine domains, thus hydrophilic/superhydrophobic patterned surfaces with efficient water collection could be successfully developed inspired by Namib Desert beetles and mussels. The bioinspired materials show the potential for real-world industrialization in a large scale, which is of great significance for providing living security for those living in areas with no access to fresh water.