Water Supply and Stormwater Management Benefits of Residential Rainwater Harvesting in U.S. Cities

This article presents an analysis of the projected performance of urban residential rainwater harvesting systems in the United States (U.S.). The objectives are to quantify for 23 cities in seven climatic regions (1) water supply provided from rainwater harvested at a residential parcel and (2) stormwater runoff reduction from a residential drainage catchment. Water‐saving efficiency is determined using a water‐balance approach applied at a daily time step for a range of rainwater cistern sizes. The results show that performance is a function of cistern size and climatic pattern. A single rain barrel (190 l [50 gal]) installed at a residential parcel is able to provide approximately 50% water‐saving efficiency for the nonpotable indoor water demand scenario in cities of the East Coast, Southeast, Midwest, and Pacific Northwest, but <30% water‐saving efficiency in cities of the Mountain West, Southwest, and most of California. Stormwater management benefits are quantified using the U.S. Environmental Protection Agency Storm Water Management Model. The results indicate that rainwater harvesting can reduce stormwater runoff volume up to 20% in semiarid regions, and less in regions receiving greater rainfall amounts for a long‐term simulation. Overall, the results suggest that U.S. cities and individual residents can benefit from implementing rainwater harvesting as a stormwater control measure and as an alternative source of water.     

A City Wide Assessment of the Financial Benefits of Rainwater Harvesting in Mexico City

We assess the potential financial benefits of rooftop rainwater harvesting (RWH) in Mexico City from the perspective of property owners and entrepreneurs. A bottom‐up approach was followed by evaluating RWH at individual buildings and aggregating the results to a borough/city level. We consider sector‐specific water demands, potable and nonpotable uses, and user‐specific water tariffs. We find that RWH is economically most beneficial for nondomestic users rather than for small domestic users, who are often the target of RWH interventions. Based on a net present value analysis, a potable RWH system is not favored for most domestic users under the current subsidized municipal water tariff structure. Our analysis only considers capital and maintenance expenses, and not other benefits related to increased access to water and reliability, or social benefits from a switch to a RWH system. If the initial capital expense for RWH is partly financed by transferring the water subsidy to an entrepreneur, then RWH becomes financially attractive for a wide range of domestic users. To improve water access in Mexico City, RWH is attractive in the most marginalized boroughs where water use is currently lower and precipitation is higher. For domestic users relying on trucked water, RWH can have great financial benefits. Our approach provides quantitative data with high spatial specificity, highlighting the places and types of users that would benefit most from RWH.     

The Impacts of Water Conservation Strategies on Water Use: Four Case Studies1

Tsai, Yushiou, Sara Cohen, and Richard M. Vogel, 2011. The Impacts of Water Conservation Strategies on Water Use: Four Case Studies. Journal of the American Water Resources Association (JAWRA) 47(4):687‐701. DOI: 10.1111/j.1752‐1688.2011.00534.x Abstract: We assessed impacts on water use achieved by implementation of controlled experiments relating to four water conservation strategies in four towns within the Ipswich watershed in Massachusetts. The strategies included (1) installation of weather‐sensitive irrigation controller switches (WSICS) in residences and municipal athletic fields; (2) installation of rainwater harvesting systems in residences; (3) two outreach programs: (a) free home indoor water use audits and water fixture retrofit kits and (b) rebates for low‐water‐demand toilets and washing machines; and (4) soil amendments to improve soil moisture retention at a municipal athletic field. The goals of this study are to summarize the effectiveness of the four water conservation strategies and to introduce nonparametric statistical methods for evaluating the effectiveness of these conservation strategies in reducing water use. It was found that (1) the municipal WSICS significantly reduced water use; (2) residences with high irrigation demand were more likely than low water users to experience a substantial demand decrease when equipped with the WSICS; (3) rainwater harvesting provided substantial rainwater use, but these volumes were small relative to total domestic water use and relative to the natural fluctuations in domestic water use; (4) both the audits/retrofit and rebate programs resulted in significant water savings; and (5) a modeling approach showed potential water savings from soil amendments in ball fields.     

CASA DEL AGUA: WATER CONSERVATION DEMONSTRATION HOUSE 1986 THROUGH 19981

ABSTRACT: Casa del Agua (Casa) in suburban Tucson, Arizona, was designed as a residential water conservation facility for applied research, demonstration of operational results, and transfer of technology to the general public. Starting in 1983, an existing residence was located, modified and retrofitted to acquire operational data on residential water use. Modifications included retrofitting existing landscapes and enlarging the rooftop to collect and harvest rainwater; separating blackwater and graywater lines; installing meters, low‐water‐use appliances and fixtures, and underground storage tanks for rainwater and graywater; and creating a public information center. Over the 13‐plus years of actual operation, both the interior and exterior water use research results indicate large reductions in water use can be effected using water‐saving devices andlor harvesting and reusing rainwater and graywater. Casa achieved over a 24 percent reduction in total water use and a 47 percent reduction in municipal water used compared to the typical Tucson residence. Overall water used was comprised of harvested rainwater (10 percent), recycled graywater (20 percent), and municipal water (70 percent). Casa's Information Center was visited by approximately 13,000 people from September 1985 through April 1999 and the research has been featured in local, national, and international media.     

The small-scale water provider in Paraguay: bringing private sector efficiency to water resource use and the provision of drinking water to the poor

This article provides a case study of small-scale private sector provision of water supply in Paraguay, where the Government has sought sector policy reforms that would encourage private investment in drinking water supply. Ironically, while the Government has focused almost entirely on garnering the interest of large private international water companies, much smaller local firms have already made significant investments in drinking water services for the poor, all without any participation or encouragement from the Government. Outside Paraguay's two major cities, Asunción and Ciudad del Este, large numbers of aguateros currently provide piped potable water to lower-income people. Though the aguateros have little legal footing — they are in many respects informal and unregulated —they have constructed as much as one third of all the new drinking water connections in these two cities over the past 20 years. The small-scale water systems in Paraguay offer a model of financial, economic, and water-use efficiency. This article asserts that an abundance of groundwater resources, cheap access to electricity for pumping, and a spirit of informal investment, among other variables, has spawned widespread use of this approach. This article documents and analyzes the features of these independent small-scale water providers in Paraguay and the efficiency they bring to the use of water resources in meeting drinking water demands among the poor. It also cautions against policies that may trample on such entrepreneurial spirit in the name of State-managed privatization.     

Unsafe waters: the hydrosocial cycle of drinking water in Western Mexico

ABSTRACT

Mexico faces multiple water quality challenges, both in terms of the water supplied to the population as well as surface and underground water sources. Problems with drinking water supply affect the population in diverse ways, from associated health risks to high levels of intermittency in service to the poor perception of the quality of piped water – leading to high levels of bottled water consumption. In this text we explore the issue of drinking water quality in three contexts in the state of Jalisco: in Guadalajara, the state’s main urban area, in the peri-urban municipality of El Salto, and in the mid-sized city of San Juan de los Lagos. Our analysis explores drinking water regulations, the water quality monitoring undertaken by state and local authorities, access to information, as well as the actions and perceptions of water service providers. Looking at cases of indirect reuse of wastewater as well as groundwater sources with high levels of fluoride and arsenic, we argue that the foregrounding of water quality is key to illuminating social inequalities in access to water and in teasing out power relations prevailing in current hydrosocial regimes. We conclude that this hydrosocial cycle of drinking water is characterised by prioritising access to water for economic actors, facilitated by lax regulations and minimal enforcement, as well as by the systematic neglect by government authorities at all levels of the protection of watersheds and aquifers, and of water quality issues generally.     

Large‐Scale Fine‐Resolution Hydrological Modeling Using Parameter Regionalization in the Missouri River Basin

This study simulated crop and water yields in the Missouri River Basin (MRB; 1,371,000 km²), one of the largest river basins in the United States, using the Soil and Water Assessment Tool (SWAT) at a fine resolution of 12‐digit Hydrological Unit Codes (HUCs) using the regionalization calibration approach. Very few studies have simulated the entire MRB, and those that have developed were at a coarser resolution of 8‐digit HUCs and were minimally calibrated. The MRB was first divided into three subbasins and was further divided into eleven regions. A “head watershed” was selected in each region and was calibrated for crop and water yields. The parameters from the calibrated head watershed were extrapolated to other subwatersheds in the region to complete comprehensive spatial calibration. The simulated crop yields at the head watersheds were in close agreement with observed crop yields. Spatial validation of the aggregated crop yields resulted in reasonable predictions for all crops except dryland corn in a few regions. Simulated and observed water yields in head watersheds and also in the validation locations were in close agreement in naturalized streams and poor agreement in streams with high groundwater‐surface water interactions and/or reservoirs found upstream of the gauges. Overall, the SWAT model was able to reasonably capture the hydrological and crop growth dynamics occurring in the basin despite some limitations.     

Modeling Hydrology in a Small Rocky Mountain Watershed Serving Large Urban Populations1

Abstract: This article describes the development of a calibrated hydrologic model for the Blue River watershed (867 km²) in Summit County, Colorado. This watershed provides drinking water to over a third of Colorado’s population. However, more research on model calibration and development for small mountain watersheds is needed. This work required integration of subsurface and surface hydrology using GIS data, and included aspects unique to mountain watersheds such as snow hydrology, high ground‐water gradients, and large differences in climate between the headwaters and outlet. Given the importance of this particular watershed as a major urban drinking‐water source, the rapid development occurring in small mountain watersheds, and the importance of Rocky Mountain water in the arid and semiarid West, it is useful to describe calibrated watershed modeling efforts in this watershed. The model used was Soil and Water Assessment Tool (SWAT). An accurate model of the hydrologic cycle required incorporation of mountain hydrology‐specific processes. Snowmelt and snow formation parameters, as well as several ground‐water parameters, were the most important calibration factors. Comparison of simulated and observed streamflow hydrographs at two U.S. Geological Survey gaging stations resulted in good fits to average monthly values (0.71 Nash‐Sutcliffe coefficient). With this capability, future assessments of point‐source and nonpoint‐source pollutant transport are possible.     

Informal privatisation of community taps: issues of access and equity

On the basis of a detailed case study this paper questions the equity of centralised piped drinking water supply systems installed by the government of Nepal in rural areas. The study shows how processes of socio-technical interaction and change alter the physical water supply infrastructure of the installed public water supply system, simultaneously altering patterns of access to taps and water. The analysis suggests that this happens through a process of “informal privatisation”, with community taps becoming appropriated by individuals over time, cutting off some families from their access to community tap water while reinforcing the water security of others. This process is deeply shaped by prevailing relations of power and cultural difference along axes of gender, caste and wealth.     

A decision model for selecting sustainable drinking water supply and greywater reuse systems for developing communities with a case study in Cimahi, Indonesia

Capacity Factor Analysis is a decision support system for selection of appropriate technologies for municipal sanitation services in developing communities. Developing communities are those that lack the capability to provide adequate access to one or more essential services, such as water and sanitation, to their residents. This research developed two elements of Capacity Factor Analysis: a capacity factor based classification for technologies using requirements analysis, and a matching policy for choosing technology options. First, requirements analysis is used to develop a ranking for drinking water supply and greywater reuse technologies. Second, using the Capacity Factor Analysis approach, a matching policy is developed to guide decision makers in selecting the appropriate drinking water supply or greywater reuse technology option for their community. Finally, a scenario-based informal hypothesis test is developed to assist in qualitative model validation through case study. Capacity Factor Analysis is then applied in Cimahi Indonesia as a form of validation. The completed Capacity Factor Analysis model will allow developing communities to select drinking water supply and greywater reuse systems that are safe, affordable, able to be built and managed by the community using local resources, and are amenable to expansion as the community's management capacity increases.     

Cost-benefit analysis of central softening for production of drinking water

Softening drinking water before distribution yields advantages with environmental impact, such as lower household products consumption, less scaling in piping and machines, and the avoidance of decentralized, domestic softeners. Central softening is under consideration in Flanders by the largest water supplier, VMW (Dutch acronym for “Flemish Company for Water Supply”), to deliver soft (15 °F) water to their customers. A case study is presented for a region with hard water (47 °F). The chosen technique is the pellet reactor, based on precipitation of CaCO₃ by NaOH addition. This softening operation has possibly large impact on the environment and the water consumption pattern.A cost-benefit analysis has been made to estimate the added value of central softening, by investigating the impact on the drinking water company, on their customers, on employment, on environment, on health, etc. The analysis for the region of study revealed benefits for customers which were higher than the costs for the drinking water company. However, pricing of drinking water remains an important problem.A sensitivity analysis of these results has also been made, to evaluate the impact of important hypothesis, and to be able to expand this study to other regions. The conclusions for this part show that softening is beneficial if water hardness is to be decreased by at least 5 °F.     

SEASONAL PUMPING VARIATION EFFECTS ON WELLHEAD PROTECTION AREA DELINEATION1

ABSTRACT: Delineation of a welihead protection area (WHPA) is the key element in welihead protection programs for drinking water supplies. WHPAs are often delineated under idealized conditions using simple steady-state assumptions, which lead to an incorrect estimation of area and geometry. In this paper, we compare the results from a simple steady-state procedure commonly employed in WHPA delineation with a more complex transient approach that allows consideration of seasonal variation in pumping rates. We also introduce a transient procedure to delineate time-related capture zones using a numerical ground water flow and transport model. Welihead delineation is examined for two municipal wells in Tipton, Oklahoma, using a ten-year time-of-travel criterion. In the steady-state procedure, where we assumed constant pumping rates, we used GPTRAC, a semi-analytical model, and MOC, a numerical model. The capture zone delineated by GPTRAC is comparable in shape with the capture zone delineated by MOC but not in size due to the differences in solution schemes. In the transient procedure, we used MOC and considered the seasonal variation in pumping rates. The capture zones delineated in this procedure were larger than the capture zones delineated by the steady-state procedure using the same model. Further analysis showed that a higher drawdown was predicted in the transient procedure than in the steady-state procedure, which is the reason for larger capture zones.     

A HYDRODYNAMIC MODELING STUDY TO DETERMINE THE OPTIMUM WATER INTAKE LOCATION IN LAKE PALDANG,KOREA1

A three‐dimensional hydrodynamic model was applied to Lake Paldang, South Korea. The lake has three inflows, of which Kyoungan Stream has the smallest flow rate and poorest water quality. Since all drinking water intake stations are located near the confluence of Kyoungan Stream within the lake, this contaminated tributary may have a significant impact on the quality of drinking water sources. The optimum drinking water intake location was determined from the applied model. The model was calibrated and verified using the data measured under different hydrological conditions. The model results were in reasonable agreement with the field measurements in both calibration and verification. The circulation and spreading patterns of the incoming flows in the lake, as well as their composition ratios to the drinking water intakes were determined from the model, and three alternative intake locations were proposed. The simulation results suggested that the horizontal and vertical relocations of the intake aqueduct could significantly decrease the composition ratio of the contaminated water. From this study, it was concluded that the three‐dimensional hydrodynamic model could successfully simulate the temporal and spatial mixing patterns of incoming flows and become a useful tool in determining the optimum water intake location in Lake Paldang.     

Regional water flows – Assessing opportunities for sustainable management

Sustainable water management may strongly benefit from an integrated approach. Additionally, an integrated urban water management policy considering the various urban water flows and the possible interactions between the water sector and the remaining urban activities can benefit if based on an urban metabolism based analysis. This article assesses water flows of Lisbon Metropolitan Area considering the conventional water supply system and wastewater treatment system flows and also the hydrological cycle flows, and proposes a global set of indicators to perform a benchmarking analysis of the 18 municipalities of the region. Results highlighted the heterogeneous nature of the Metropolitan area in terms of water management – either in terms of management entities (predominantly public or municipalized), water consumption (varying from 227.4 l/hab.day in Palmela to 402.7 l/hab.day in Seixal), wastewater treatment (10 out of 18 municipalities already undergo secondary or tertiary wastewater treatments), runoff indices (depending on the municipality's level of urbanization), among other. Through the output volumes it was also assessed the potential of the municipalities to reuse wastewater for potable or non-potable urban uses, as well as the potential to harvest and harness rainwater. The main constraints to an integrated water management were identified and some potential solutions were measured and proposed even though they need further assessment, particularly in a cost-benefit perspective.     

Do disinfection byproducts in drinking water have an effect on human cancer risk worldwide? A meta‐analysis

In the present study, a meta‐analysis was carried out to clarify the association between disinfection byproducts (DBPs) in drinking water and human cancer risk worldwide. Kidney, colorectal, esophagus, urinary bladder, brain, breast, leukemia, lung, and rectum cancers were selected to perform this analysis. According to preferred reporting items for systematic review and meta‐analysis protocol (PRISMA) guidelines, the relevant studies were identified and selection criteria (inclusion and exclusion criteria) were applied. Next, effective subgroups in these studies (gender, type of drinking water source, and type of DBPs) were analyzed. The quality of the studies was evaluated using the Newcastle‐Ottawa Scale. In addition, this overall study included analyses of 16 case–control and 3 cohort studies. The overall odds ratio (OR) with 95% confidence intervals (CI) between DBPs and cancer risk was 1.01 (95% CI, 0.94–1.09). The summary ORs of cancer risk were 1.04 (95% CI, 0.89–1.19) for kidney; 0.98 (95% CI, 0.87–1.09) for colorectal; 1.07 (95% CI, 0.84–1.29) for esophagus; 0.93 (95% CI, 0.80–1.06) for pancreatic; 1.00 (95% CI, 0.83–1.18) for brain; 1.13 (95% CI, 0.99–1.26) for breast; 0.93 (95% CI, 0.72–1.13) for leukemia; and 1.18 (95% CI, 1–1.36) for lung cancers. The results of this meta‐analysis suggested that there is not a significant association between DBPs in water and cancer risk. In addition, subgroup analysis shows a positive association with colorectal and kidney cancer risk in men, as well as colon and breast cancers in females. Studies of both genders have shown a significant association between lung and pancreatic cancers. Moreover, this study finds a significant relationship between cancer rate and consumers of city water and bottled water sources. In analyzing different types of DBPs in water, chlorine and trichloromethane show a significant association in increasing cancer risk.     

Applying exergy analysis to rainwater harvesting systems to assess resource efficiency

In our continued effort in reducing resource consumption, greener technologies such as rainwater harvesting could be very useful in diminishing our dependence on desalinated or treated water and the associated energy requirements. This paper applies exergy analysis and exergetic efficiency to evaluate the performance of eight different scenarios of urban rainwater harvesting systems in the Mediterranean-climate Metropolitan Area of Barcelona where water is a scarce resource. A life cycle approach is taken, where the production, use, and end-of-life stages of these rainwater harvesting systems are quantified in terms of energy and material requirements in order to produce 1 m³ of rainwater per year for laundry purposes. The results show that the highest exergy input is associated with the energy uses, namely the transport of the materials to construct the rainwater harvesting systems. The scenario with the highest exergetic efficiency considers a 24 household building with a 21 m³ rainwater storage tank installed below roof. Exergy requirements could be minimized by material substitution, minimizing weight or distance traveled.     

Estimating Forest Ecosystem Evapotranspiration at Multiple Temporal Scales With a Dimension Analysis Approach1

Abstract:  It is critical that evapotranspiration (ET) be quantified accurately so that scientists can evaluate the effects of land management and global change on water availability, streamflow, nutrient and sediment loading, and ecosystem productivity in watersheds. The objective of this study was to derive a new semi‐empirical ET modeled using a dimension analysis method that could be used to estimate forest ET effectively at multiple temporal scales. The model developed describes ET as a function of water availability for evaporation and transpiration, potential ET demand, air humidity, and land surface characteristics. The model was tested with long‐term hydrometeorological data from five research sites with distinct forest hydrology in the United States and China. Averaged simulation error for daily ET was within 0.5 mm/day. The annual ET at each of the five study sites were within 7% of measured values. Results suggest that the model can accurately capture the temporal dynamics of ET in forest ecosystems at daily, monthly, and annual scales. The model is climate‐driven and is sensitive to topography and vegetation characteristics and thus has potential to be used to examine the compounding hydrologic responses to land cover and climate changes at multiple temporal scales.     

HEALTH RISKS ASSOCIATED WITH CONSUMPTION OF UNTREATED WATER FROM HOUSEHOLD ROOF CATCHMENT SYSTEMS1

ABSTRACT: Rainwater harvesting is receiving increased attention worldwide as an alternative source of drinking water. Although collected rainwater is typically consumed without any type of disinfection, the microbial quality of this type of water source can be poor. Around the world, consumers of collected and stored rainwater may be at considerable risk to a variety of infectious diseases. This review presents studies attributing specific risks of diseases to the consumption of contaminated rainwater. Diseases attributed to the consumption of untreated rainwater include bacterial diarrheas due to Salmonella and Campylobacter, bacterial pneumonia due to Legionella, botulism due to Clostridium, tissue helminths, and protozoal diarrheas from Giardia and Cryptosporidium. Simple indicator systems such as fecal coliform measurements may prove to be inadequate for determining microbial risks associated with consumption of water from rainwater catchment systems.     

Sustainable Rainwater Catchment Systems for Micronesian Atoll Communities

Atoll island communities rely on rainwater catchment systems (RWCS) as a primary method of storing freshwater. However, stored freshwater can be depleted during times of drought, requiring importation of water to sustain community living. To maintain adequate water supply under future climatic conditions, the functioning of RWCS for atoll communities must be analyzed and optimal designs must be adopted. In this study, a quantitative analysis of stored daily water volumes is provided for atoll islands within the Federated States of Micronesia (FSM), with Nikahlap Island, Pakein Atoll, and a generic island in western FSM used as representative cases. Using a daily water balance model for the RWCS, baseline conditions are simulated for the 1997‐1999 time period, during which an intense El Niño‐induced drought occurred, and a sensitivity analysis is performed to quantify the influence of RWCS features on water system outputs, whereupon an optimal RWCS design using existing infrastructure is analyzed. Results indicate the strong influence of catchment area, system efficiency, and storage capacity on water volumes and the depletion of water during dry seasons and drought periods using current RWCS infrastructure. Adequate storage can be maintained during a major drought if unused RWCS features are employed and if minimal rationing is adopted. Study results provide water resource managers and government officials with valuable data for consideration in water security measures.     

County‐Scale Rainwater Harvesting Feasibility in the United States: Climate,Collection Area,Density, and Reuse Considerations

Roof rainwater harvesting (RWH) has the potential to augment water supplies for urban and suburban uses throughout the United States (U.S.). Studies of the performance of RWH at the building and city scales in the U.S. are available, but a countrywide overview of the potential performance of RWH at the county scale has not been done before. Three approaches were taken: (1) assess the viability of RWH in terms of the rainfall that could be captured in relation to the water demand in each county (excluding agriculture), (2) evaluate the performance of a “typical” domestic RWH system across all counties with metrics related to its ability to supply the potable and nonpotable demand, and (3) evaluate the effect of adding a 50% rainwater reuse component to the analysis. We find RWH could be a viable supplemental water source in the U.S., particularly in counties of the Pacific Northwest, Central, and Eastern regions (percent demand covered >50%). Low population density counties have the potential to meet their annual water needs with RWH, while high‐density counties could only source a small portion (~20%) of their annual demand with RWH. Typical RWH systems in counties in the Central and Eastern U.S. performed better than in Western counties. Adding a reuse component can be a key factor in making RWH attractive in many areas of the country. This work can inform future water infrastructure investment and planning in the U.S.