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©2019. The Authors. Nearly one billion people worldwide receive water through piped networks that are not continually pressurized and operate intermittently. The prevalence and persistence of these Intermittent Water Supplies (IWS) is surprising as this mode of operation induces water contamination and customer equity issues. Shortages of source water, customers' water demand, and leaking pipes are frequently cited as necessitating IWS. We propose a framework for understanding the persistence and operation of IWS. The supply system is represented by an average customer and a spatially averaged leakage rate. With this macroscopic hydraulic model, we relate customer demand satisfaction, source water availability, customer demand, and leakage. While this approach ignores the complexities of network topology, we find that the model approximates real systems well (calibrating to four intermittent reference networks achieved R2>0.87). The calibrated model is robust to moderate changes in demand and leakage (maintaining R2>0.81). Using the model, we show that the tipping point between satisfied demand and unsatisfied demand is a local optimum for utilities, which may explain the persistence of IWS. Beyond this point, the volume received by customers does not increase, but utilities must supply more water to the network. The generality of the proposed model enables its use when regulating and upgrading IWS. We demonstrate the latter by critiquing a performance-based contract that was intended to improve an intermittent supply in India. Demand satisfaction has profound implications for hydraulics and human welfare. We propose the degree of demand satisfaction as a metric for evaluating IWS and for tracking the United Nations Sustainable Development Goal 6.1.

A new perspective on carbon economics is developed and applied to demonstrate that oil and natural gas producers in North Dakota (ND) have an opportunity to make a profitable transition to wind energy producers. ND's oil and gas producers can fund this black into green (BIG) transition by: first, investing a fraction of their revenues into wind energy farms; and second, reinvesting a portion of revenues from the wind-generated electricity. Over a period of 40 years, 100% of the greenhouse gas emissions associated with the production and consumption of ND's oil and gas could be offset with an investment of 10% of both hydrocarbons’ value and a reinvestment of three cents per kilowatt-hour of wind-generated electricity. At the end of the 40-year period, the resultant 155-gigawatt wind farm would have offset 13.4 × 109 tons of carbon dioxide equivalent and cost $9.90/ton of offset carbon dioxide equivalent. This BIG example demonstrates the financial and environmental benefits of ND's oil and gas producers transforming into renewable energy producers; hence regulators, hydrocarbon producers, and utilities should take note and think BIG. The reconfigurable, Excel-based model used herein is provided to allow readers to extend this example from ND to other regions, hydrocarbons, and green energy sources.

Carbon taxes are frequently proposed as a means to mitigate the hydrocarbon industry's environmental impact. This paper assesses the potential benefits of an alternative to carbon taxes (ACT), where hydrocarbon producers directly invest a fixed amount per unit produced into renewable energy systems (e.g., wind farms). Producers maintain ownership of the assets and reinvest a portion of revenue from them to further grow the renewable assets. This proposal could help producers gradually evolve from hydrocarbon to renewable energy companies – avoiding the job losses associated with sudden industry shifts. We present an in-depth case study of the Athabasca oil sands, and extend the results to other regions. We find that wind turbines purchased with an ACT of 12/barrel where 0.03/kWh of produced power is reinvested could offset all the greenhouse gas emissions from extracting and refining the region's bitumen, provided wind turbines were located at good wind sites. Finally, to increase the grid's ability to use the wind power generated, energy storage and grid systems should also be an option for ACT investing. Future work should focus on North Dakota, which has extensive hydrocarbon resources collocated with good wind resources. Keywords: Oil sands; Emissions; Wind power; Greenhouse gas

Intermittent water supplies (IWS) deliver piped water to one billion people; this water is often microbially contaminated. Contaminants that accumulate while IWS are depressurized are flushed into customers’ homes when these systems become pressurized. In addition, during the steady-state phase of IWS, contaminants from higher-pressure sources (e.g., sewers) may continue to intrude where pipe pressure is low. To guide the operation and improvement of IWS, this paper proposes an analytic model relating supply pressure, supply duration, leakage, and the volume of intruded, potentially-contaminated, fluids present during flushing and steady-state. The proposed model suggests that increasing the supply duration may improve water quality during the flushing phase, but decrease the subsequent steady-state water quality. As such, regulators and academics should take more care in reporting if water quality samples are taken during flushing or steady-state operational conditions. Pipe leakage increases with increased supply pressure and/or duration. We propose using an equivalent orifice area (EOA) to quantify pipe quality. This provides a more stable metric for regulators and utilities tracking pipe repairs. Finally, we show that the volume of intruded fluid decreases in proportion to reductions in EOA. The proposed relationships are applied to self-reported performance indicators for IWS serving 108 million people described in the IBNET database and in the Benchmarking and Data Book of Water Utilities in India. This application shows that current high-pressure, continuous water supply targets will require extensive EOA reductions. For example, in order to achieve national targets, utilities in India will need to reduce their EOA by a median of at least 90%.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Cataloged from PDF version of thesis., Includes bibliographical references (pages 151-155)., Intermittently-operated water systems struggle to equitably and effectively distribute clean water to customers. One common customer response to intermittency is to supplement the water system's pressure by using a household, or residential, booster pump. When such booster pumps are directly connected to the water utility's supply pipe, without an underground isolation tank (sump), they often induce negative pressure in the supply pipe which increases the flow rate. Unfortunately, where leakage rates are high, this negative pressure also increases the risk of contaminant intrusion. This thesis presents the iterative design and field testing of a patent-pending, full-bore, back-pressure regulating valve. The valve's simple mechanism relies on a stabilized collapsing tube, or 'Starling Resistor,'which when installed at a customer's connection, controls the flow rate and prevents booster pumps from creating negative pressure in the supply pipe. In collaboration with the Delhi Jal Board and several private partners, the valve's performance was verified in two rounds of field trials in neighborhoods of New Delhi, India including Pitampura, Azad Market, Vivek Vihar, Malvia Nagar, and Vasant Vihar. Using a crossover study, the valve was found to reduce the total contamination risk across all 19 tested houses during supply times by a median of 80%. The valve prevented 96% of pressure below -1 meter and an average of 53 minutes per day, per connection of total negative pressure. In an estimated worst-case scenario for contaminant intrusion, the presence of the valve reduced the contamination risk by two orders of magnitude at six customer connections - enough to correspond to significant reductions in health risks., by David Donald James Taylor., S.M.