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Rainwater harvesting (RWH) is perhaps the most ancient practice to meet water supply needs. It has received renewed attention since the 1970s as a productive water source, water savings and conservation means, and sustainable development tool. In RWH, it is important to know how much water can be harvested at a given location from a given catchment size, whether the harvested water meets the intended water quality, whether the RWH system is economically viable and whether the state regulations favor the RWH. Furthermore, the selected RWH system should be suitable to local rainfall and field conditions, downstream impacts, and socio-economic and cultural characteristics. In this regard, this paper provides an overview of the special issue on "Rainwater Harvesting: Quantity, Quality, Economics and State Regulations". The selected papers cover a wide range of issues that are relevant to RWH such as regionalization of design curves, use of spatial technology, urban agriculture, arid-region water supply, multi criteria analysis and application of artificial neural networks. [ABSTRACT FROM AUTHOR]

The paper proposes a semi-probabilistic approach for the design of rainwater tanks. In particular, the cumulative distribution function of the active storage is derived as a function of rainfall moments. The model is validated through continuous simulation of the hydraulic behaviour of a hypothetical rainwater tank located in Milan (North Italy) using as input a series of rainfall records. [ABSTRACT FROM AUTHOR]

A methodology for the estimation of household potable water saving due to internally plumbed rainwater tanks (IPT) is presented in this paper. The methodology is based on a pairwise comparison of household water billing data between homes with IPT and without rainwater tanks (No Tank). These savings were compared with estimations using measured end use data and rainwater demand predictions using the Rainwater TANK model. The paper describes the application of this methodology to a case study in the south-east Queensland (SEQ) region of Australia. There was a significant reduction in mains water consumption for IPT properties in all regions studied in SEQ. Water reductions from mains supplies varied markedly across regions with mean values ranging from 20 to 95 kL/hh/y with an average mean of 50 kL/hh/y. Median water consumption values, ranged in mains water reductions from 28 to 52 kL/hh/y, with an average median of 40 kL/hh/y. Considering both measures an average water saving between 40 and 50 kL/hh/y can be expected from internally plumbed rainwater tanks. Water restrictions appear to have a strong influence on estimated reductions in mains water use. In regions where water restrictions were severe, water consumption was less varied between No Tank and IPT homes with a consequent reduction in estimated savings observed. Recommendations for further work include a survey to capture confounding factors that could not be fully controlled in the desktop study and a controlled pairwise experiment to monitor water consumption from raintanks. [ABSTRACT FROM AUTHOR]

Water is a scarce resource in arid regions, and hence water harvesting is critically important in these regions for which many different means are adopted including groundwater and rainwater harvesting. This paper examines the feasibility of rainwater harvesting from roof catchments in arid regions of Australia. For this, ten representative locations in the arid regions of Australia are selected. Also, ten different sizes of rainwater tanks ranging from 5 kL to 50 kL and three different combinations of water uses are considered. A model is developed to simulate the performance of a rainwater harvesting (RWH) system. It is found that the reliability of a RWH system is highly dependent on mean annual rainfall at the location of interest. It is found that a 20 kL tank can provide a reliability of 61%–97% for toilet and laundry use depending on the location within the Australian arid regions. At the current water price, RWH system is not financially viable in the Australian arid regions. The methodology adopted in this paper can be adapted to other similar arid regions of the world. [ABSTRACT FROM AUTHOR]

Rainwater tanks are a fundamental component of integrated water cycle management, but the quality of harvested water is little understood and is potentially affected by many factors such as roofing material, site temperature, frequency of tank use, and surrounding land use. There has been limited study of the first flush, overflow water and harvested water quality from rainwater tanks in Australia. This paper presents the water quality results of a yearlong data collection and analysis study involving five rainwater tanks located in Western Sydney, Australia. The results show that tank water quality was impacted by the construction materials used to fabricate both the tanks and roofs. Furthermore, the overflow and first flush water quality were found to be of a lower standard than the tank samples, with implications for the cleaning of the first flush device and overflow diversion. Finally, the issues identified with the maintenance of the tanks are highlighted and discussed. [ABSTRACT FROM AUTHOR]

Melbourne, Australia faced fourteen consecutive years of below average rainfall before drought breaking rains in 2010. Melbournians are also concerned about the significant increase in potable water price in the future where the cost is expected to increase by 100% in 5 years. Stormwater harvested using rainwater tanks is an alternative source of nonpotable water source where potable quality water is not required for use. However, prior to installing rainwater tanks, customers expected to investigate the financial viability of installing tanks. The objective of this study is to carry out cost effectiveness analysis to estimate the payback period, cost effectiveness ratio and the levelized cost of installing rainwater tanks in different geographical locations with significantly varying mean annual rainfall (MAR). The paper also focuses on the impact of the inflation rate, interest rate (discount rate), the period of analysis on the previously stated cost parameters and determines the optimum tank size based on the MAR of the location. The study showed that the payback period was as low as 14 years for a 5kL tank in an area where the MAR is around 1000 mm (discount rate of 10% and inflation rate of 4.2%). The payback period varied considerably with the tank size especially in low rainfall areas (MAR ≤ 450 mm). This emphasizes the importance of selecting the optimum tank size to ensure maximum use of the rainwater to maximize the return on the initial investment. [ABSTRACT FROM AUTHOR]

A Water Sensitive City is now commonly acknowledged best practice for designing the cities of the future. In Australia, the National Water Initiative has allocated high priority towards offering insight into successful water sensitive urban development projects, to facilitate capacity building within the industry. This paper shares innovative water sensitive projects implemented at Kogarah City Council, in Sydney. Four key projects are discussed, demonstrating how stormwater, rainwater and wastewater can be incorporated into decentralised water systems to offer sustainable water management of the future. The case studies included in the paper highlight Kogarah's journey towards the Soft Path for Water Management. [ABSTRACT FROM AUTHOR]

Rainwater harvesting in residential homes is emerging as an important complement to centralized water supplies in urban centres around the world. Domestic rainwater harvesting systems provide a variety of benefits for water management and contribute to sustainable and integrated urban water management. There are however risks associated with rainwater harvesting that requires appropriate mitigation. One such risk is that systems can become breeding grounds for mosquitoes. This can constitute a significant health risk through the spread of mosquito-borne diseases (i.e. arbovirus and malaria). This paper explores the extent to which mosquitoes breed in rainwater harvesting systems as well as the effectiveness of different risk mitigation actions. Data were sourced from a large-scale domestic rainwater tank inspection survey undertaken in Melbourne and were analysed using simple Bayesian Network models. The observed rate of mosquito breeding was too high and was identified as a serious concern for health officials and water managers. The most common access routes into the tank system were found to be through the tank inlet or overflow. By exploring different system set-ups it was found that in order to mitigate the risk of mosquito breeding in tanks, all potential access routes must be adequately sealed. The complete eradication of mosquitos in rainwater tanks, however, may need further investigation, as 4% of systems with adequate protection at the inlet and overflow were still found to have mosquitoes in them. [ABSTRACT FROM AUTHOR]

Rainwater tanks are increasingly being implemented as part of the integrated urban water management paradigm where all sources of water, including potable, stormwater and recycled, are considered eligible to contribute to the urban water supply. Over the last decade or so, there has been a rapid uptake of rainwater tank systems in urban areas, especially in Australian cities, encouraged through financial incentives, but more importantly, from change in residential building codes effectively mandating the installation of rainwater tanks. Homes with rainwater tanks in Australian cities have increased from 15% to 28% over six years to 2013. These building codes specify certain rainwater tank specifications to achieve a stated rainwater use, and hence potable water savings. These specifications include minimum rainwater tank size, minimum connected roof area, plumbing for internal supply for toilets and washing machines, and external supply for garden watering. These expected potable water savings from households are often factored into regional strategic water planning objectives. Hence if rainwater tanks do not deliver the expected saving due to sub-standard installation and/or poor maintenance, it will have an adverse impact on the regional water plan in the longer term. In this paper, a methodology to assess the effectiveness of a government rainwater tank policy in achieving predicted potable water savings is described and illustrated with a case study from South East Queensland, Australia. It is anticipated that water professionals across the globe should be able to use the same methodology to assess the effectiveness of similar rainwater policies, or indeed any other distributed water saving policy, in their local planning communities. [ABSTRACT FROM AUTHOR]

Rainwater harvesting (RWH) is perhaps the most ancient practice to meet water supply needs. It has received renewed attention since the 1970s as a productive water source, water savings and conservation means, and sustainable development tool. In RWH, it is important to know how much water can be harvested at a given location from a given catchment size, whether the harvested water meets the intended water quality, whether the RWH system is economically viable and whether the state regulations favor the RWH. Furthermore, the selected RWH system should be suitable to local rainfall and field conditions, downstream impacts, and socio-economic and cultural characteristics. In this regard, this paper provides an overview of the special issue on “Rainwater Harvesting: Quantity, Quality, Economics and State Regulations”. The selected papers cover a wide range of issues that are relevant to RWH such as regionalization of design curves, use of spatial technology, urban agriculture, arid-region water supply, multi criteria analysis and application of artificial neural networks.

The objective of the paper is to evaluate the potential of tank-based rainwater harvesting systems as source control methods to mitigate runoff flow peaks in urban areas. Water balance simulations of the rainwater tanks at the resolution time scale of 1 minute were carried out for this purpose using both high-resolution rainfall series and toilet water demand data from a previous experimental campaign, which involved six experimental households in southern Italy. Simulations show that significant reduction of the flow peak may be obtained with rainwater tanks depending on the tank size and on the household water demand. [ABSTRACT FROM AUTHOR]

Lot scale rainwater tank system modeling is often used in sustainable urban storm water management, particularly to estimate the reduction in the storm water run-off and pollutant wash-off at the lot scale. These rainwater tank models often cannot be adequately calibrated and validated due to limited availability of observed rainwater tank quantity and quality data. This paper presents calibration and validation of a lot scale rainwater tank system model using XP-SWMM utilizing data collected from two rainwater tank systems located in Western Sydney, Australia. The modeling considers run-off peak and volume in and out of the rainwater tank system and also a number of water quality parameters (Total Phosphorus (TP), Total Nitrogen (TN) and Total Solids (TS)). It has been found that XP-SWMM can be used successfully to develop a lot scale rainwater system model within an acceptable error margin. It has been shown that TP and TS can be predicted more accurately than TN using the developed model. In addition, it was found that a significant reduction in storm water run-off discharge can be achieved as a result of the rainwater tank up to about one year average recurrence interval rainfall event. The model parameter set assembled in this study can be used for developing lot scale rainwater tank system models at other locations in the Western Sydney region and in other parts of Australia with necessary adjustments for the local site characteristics. [Copyright &y& Elsevier]

Decentralised water and wastewater systems are being implemented to meet growing demand for municipal services either in combination with centralised systems or as standalone systems. In Australia, there has been increased investment in decentralised water and wastewater systems in response to the capacity constraints of existing centralised systems, an extended period of below average rainfall, uncertainly in traditional water sources due to potential climate change impacts, and the need to reduce the environmental impact of urban development. The implementation of decentralised water systems as a mainstream practice at different development scales is impeded by the knowledge gaps on their actual performance in a range of development types and settings. As the wide-spread uptake of these approaches in modern cities is relatively new compared to centralised approaches, there is limited information available on their planning, design, implementation, reliability and robustness. This paper presents a number of case studies where monitoring studies are under way to validate the performance of decentralised water and wastewater systems. The results from these case studies show the yield and reliability of these decentralised systems, as well as the associated energy demand and ecological footprint. The outputs from these case studies, and other monitoring studies, are important in improving decentralised system design guidelines and developing industry wide management norms for the operation and maintenance of decentralised systems. [ABSTRACT FROM AUTHOR]

This paper provides the first published post-installation analysis of retrofitted rainwater tanks and their effects on mains water consumption. The study aimed to determine the average mains water reductions achieved in households with recently installed rainwater tanks and compare this figure with wider community consumption. The social and cultural impacts of rainwater tank ownership were also explored to understand how rainwater is used and perceived. The results show that during the period of analysis, the drought years of 2005-2007, 7125 or 8% of Illawarra households installed a tank. Comparison of mains water consumption for two years before and after installation shows that rainwater tank households reduced their mains water consumption about the same amount (10.26%) as the wider community (10.8%). The social and cultural components reveal three main groups of households. The largest group, water users, had a desire for water autonomy and independence to continue previously enjoyed water practices that had been restricted. Among a light green group, tanks were part of a package of overtly pro-environmental behaviours that did not necessarily change consumption patterns. A frugal group, many of whom had been raised in rural areas, were the main water savers. Perception of tank water quality was shown to be an influential determinant of how rainwater was used, particularly for connections internal to the house. This study shows that rainwater tanks have the potential to achieve significant water savings, but if water-intensive behaviours are not modified, and rainwater tanks are not plumbed indoors, the potential of this alternative water source will not be met. Currently, rainwater tanks facilitate water users as much as water savers. [ABSTRACT FROM AUTHOR]

Rainwater tanks are increasingly adopted in Australia to reduce potable water demand and are perceived to reduce the volume of stormwater discharge from developments. This paper investigates the water balance of rainwater tanks, in particular the possible impacts these tanks could have in controlling the stormwater discharge volume. The study collected water quantity data from two sites in the Hawkesbury City Council area, New South Wales, Australia and utilised the collected data in a simple water balance model to assess the effectiveness of rainwater tanks in reducing the stormwater discharge volume. The results indicate that a significant reduction in discharge volume from a lot scale development can be achieved if the rainwater tank is connected to multiple enduses, but is minimal when using irrigation alone. In addition, the commonly used volumetric runoff coefficient of 0.9 was found to over-estimate the runoff from the roof areas and to thereby underestimate the available volume within the rainwater tanks for retention or detention. Also, sole reliance on the water in the rainwater tanks can make the users aware of their water use pattern and water availability, resulting in significant reductions in water use as the supply dwindles, through self imposed water restrictions. [ABSTRACT FROM AUTHOR]

Abstract: Due to greater environmental awareness and mandatory water restrictions in many Australian cities, rainwater tanks have become popular in recent years. This paper investigates the water savings potential of rainwater tanks fitted in detached houses at 10 different locations in Greater Sydney, Australia. A water balance simulation model on daily time scale is developed and water savings, reliability and financial viability are examined for three different tank sizes, 2kL, 3kL and 5kL. It is found that the average annual water savings from rainwater tanks are strongly correlated with average annual rainfall. It is also found that the benefit cost ratios for the rainwater tanks are smaller than 1.00 without government rebate. It is noted that a 5kL tank is preferable to 2kL and 3kL tanks and rainwater tanks should be connected to toilet, laundry and outdoor irrigation to achieve the best financial outcome for the home owners. The results from this study suggest that government authorities in Sydney should maintain or possibly increase the rebate for rainwater tanks to enhance its acceptance. [Copyright &y& Elsevier]

Perceptions of the quality of roof harvested rainwater remain an impediment to widespread implementation of rainwater tanks on urban allotments. Previous literature reports on roof water quality have given little consideration to the relative significance of airborne environmental micro-organisms to roof catchment contamination and the issue of tank water quality. This paper outlines the findings of a recent study into the influence of weather on roof water contamination conducted at an urban housing development in Newcastle, on the east coast of Australia. Samples of direct roof run-off were collected during a number of separate rainfall events, and microbial counts were matched to climatic data corresponding to each of the monitored events. Roof run-off contamination was found to be under the strong influence of both wind speed and direction. The preliminary findings of an investigation currently under way into the microbial diversity of rainwater harvesting systems have also been presented. The results indicate that the composition of organisms present varied considerably from source to source and throughout the collection system. In all eases, evidence of faecal contamination was found to be negligible. The implications of these findings to the issues of tank water quality, health risk analysis and monitoring protocols have been discussed. [ABSTRACT FROM AUTHOR]

Rainwater harvesting (RWH) has become a popular water saving and conservation means across the globe. In many cities, a pre-determined rainwater tank size is generally selected without a detail water balance modelling at the location on interest. However, to achieve maximum benefit from a RWH system at a given location, it is desirable to design the system based on the site specific conditions (e.g. local rainfall and loss characteristics) and other relevant design parameters. There have been limited studies on regionalization of RWH system, which can account for the spatial variability in rainfall, loss and water demand characteristics over a given region to provide site-specific design of RWH system. This paper presents a RWH regionalization approach to develop a set of design curves, which assist in the selection of an adequate RWH system at a given location. We use rainfall data from 159 rain gauges across the Greater Sydney region in Australia to develop and test the proposed regionalization approach. It has been found that there is a significant variation in rainfall characteristics across Greater Sydney region and that a common tank size across this region does not present an adequate solution. It has been found that a 5 kL tank can achieve a reliability (i.e. percentage of days the RWH can meet the given demand) of 31–93% for four people depending on the location in the Greater Sydney region and the types of water use. The developed regional design curves could result in increased water savings across Greater Sydney. The proposed regionalization approach can be adapted to other cities across Australia and the world which present a high rainfall gradient. • Water savings by rainwater harvesting at 159 locations in Sydney are evaluated. • Reliability of a rainwater tank is moderately correlated with mean annual rainfall. • A set of design curves is developed for Sydney to enhance rainwater harvesting. [ABSTRACT FROM AUTHOR]

Rainwater tanks are increasingly being implemented as part of the integrated urban water management paradigm where all sources of water, including potable, stormwater and recycled, are considered eligible to contribute to the urban water supply. Over the last decade or so, there has been a rapid uptake of rainwater tank systems in urban areas, especially in Australian cities, encouraged through financial incentives, but more importantly, from change in residential building codes effectively mandating the installation of rainwater tanks. Homes with rainwater tanks in Australian cities have increased from 15% to 28% over six years to 2013. These building codes specify certain rainwater tank specifications to achieve a stated rainwater use, and hence potable water savings. These specifications include minimum rainwater tank size, minimum connected roof area, plumbing for internal supply for toilets and washing machines, and external supply for garden watering. These expected potable water savings from households are often factored into regional strategic water planning objectives. Hence if rainwater tanks do not deliver the expected saving due to sub-standard installation and/or poor maintenance, it will have an adverse impact on the regional water plan in the longer term. In this paper, a methodology to assess the effectiveness of a government rainwater tank policy in achieving predicted potable water savings is described and illustrated with a case study from South East Queensland, Australia. It is anticipated that water professionals across the globe should be able to use the same methodology to assess the effectiveness of similar rainwater policies, or indeed any other distributed water saving policy, in their local planning communities.

In Australia, water scarcity has resulted in the need for re-evaluating demand management policies, as well as the identification of alternative water supplies. Specifically, water utilities have been focusing on increasing the adoption of household level decentralised water systems (DWS). While such engineering solutions may be effective, understanding the factors which influence adoption is crucial for widespread uptake. Protection Motivation (PM) theory was used to assess DWS adoption in a sample of 295 homeowners across South East Queensland, Australia. Results provided good support for the application of PM theory to understanding whether people cope adaptively to water shortage threats. The model’s hypothesised link between adaptive coping and behavioural intention was also supported, suggesting PM theory can be used to understand people’s intention to adopt DWS in the context of the drought. The predictive ability of the PM model improved significantly when demographic variables – age and perceived water – use were included. [ABSTRACT FROM PUBLISHER]

Secure and sanitary water supply is essential for human health and well-being. The challenges in meeting this demand are great in Small Island Developing States where water resources may be limited due to social and environmental constraints. In Honiara, Solomon Islands, a number of factors have constrained access to fresh water including: rapid population growth and urbanisation; neglected water infrastructure; the ethnic tensions; water tariff increases of 170% in the past 3 years; sole reliance on groundwater; and poor supporting electrical infrastructure. Within this context, the case for using rainwater tanks as either a predominant source or for augmentation of existing domestic water supply has been explored. The effect of historical drought events on rainwater tanks has been examined. A water balance model has been developed and various household scenarios reviewed to determine the reliability of domestic rainwater tanks over a 28-year period. The development of this model has highlighted both opportunities and limitations in Honiara that can be used to inform decision-makers and planners in water resources management. [ABSTRACT FROM AUTHOR]

Over the course of Australia's Millennium Drought, urban water managers gained more appreciation of householders' willingness and capacities to respond to water shortages and restrictions, including by installing rainwater tanks (RWTs) for watering gardens. How urban water managers regard tanks and tank users gives insight into their understandings of social sustainability, as found in interviews conducted in 2006 and 2010. These also revealed a growing distance between policymakers and water providers pursuing a broader approach to sustainability in their communities. The RWT is considered here as a limit case for paradigms of urban water management: it challenges conventional distinctions (such as provider/consumer) and heralds a new hydropolitics. These challenges are discussed as seven kinds of trouble with tanks: (1) incompatibility with the management model and vision of modernity enshrined in the ideal of centralised provision in control of accredited water experts; (2) anxieties about control and risk aroused by these private on-site facilities and their non-expert users; (3) equivocation over their environmental effects, normally assessed in hydrological terms that downplay the benefits of green streetscapes; (4) inexplicability of their popularity within dominant economically rationalist models of customers; (5) educational effects that exceed rationalist, individualist models of learning and require more socially realistic, culturally intelligent and practice-oriented approaches; (6) generation of enthusiasms that are spurned as threats to rationality instead of harnessed to energise the sustainability journey and (7) community-building effects that are unthinkable within the neoliberal customer paradigm but graspable to water managers through lay concepts like “dinner table conversations”. [ABSTRACT FROM PUBLISHER]

Over the past decade, there has been rapid installation of domestic rainwater tanks in many Australian cities in response to drought, and facilitated by subsidies and development regulations. Tanks have been portrayed as a challenge to the dominance of 'big water' and a means of elevating routine interactions with water to a practical consciousness that can stimulate lasting changes in the way that water is consumed. Telephone surveys and focus groups were used to identify the ways that households that have acquired tanks, either by choice or through development conditions, interact with their tank water. Meaning was attributed to tank water in at least three distinct ways that highlight the lack of maturity of domestic rainwater tanks as an acceptable technology. Some saw the water as a personal supply to safeguard their lifestyle against restrictions. Others understood their tanks as a personal contribution to the communal environment by reducing dependence on mains water supply. The third group regarded the tank as an extension of the water supply infrastructure. The existence of mandatory connections from tanks to internal infrastructure, such as toilet and laundry facilities, correlated strongly with the likelihood that tank water was not seen as a personal resource. Tanks perpetuate the distinction between basic water supplies and luxury water that was established during water restrictions under drought conditions. [ABSTRACT FROM AUTHOR]