Harvesting Rain: System Design for Strategic Rainwater Capture
Conserving water through rainwater harvesting saves natural resources, providing water for use in buildings and for site irrigation.
Pumps and Controls
Household water pressure can be obtained in a rainwater harvesting system by the use of pumps, pressure tanks and switches. Pumps draw and pressurize water from a storage tank to channel it into a piping network or additional storage tanks. On-demand pressure tanks are included as needed. Pumps need to be sized to deliver the flow and pressure required by a plumbing system, particularly for toilets. In both cases, backflow preventers are required. In all cases piping for drinking water should never be connected to the rainwater system used for equipment and mechanical systems in buildings to avoid contamination. A rainwater storage tank can be thought of as a well even if it is above ground. A properly sized pump will function as a domestic well pump supplying water on an as needed basis.
Water Quality and Treatment
Children learn about ecology as they pass this rainwater harvesting system which is prominently placed at the entrance to Pine Crest School in Fort Lauderdale, Florida.
Chart courtesy of BRAE
Rain is part of the hydrologic cycle of the earth. The sun heats water in oceans, water evaporates and becomes water vapor and plants add water to the atmosphere through evapotranspiration. As air currents move water vapor around the earth, the water particles collect, collide and fall back to the earth as rain and snow. Rainwater that falls on roof surfaces is relatively uncontaminated and studies have shown that most rainwater can be easily treated for indoor and outdoor uses.
For outdoor irrigation, some states require the rainwater to be treated to the same standards as graywater when applied to above ground irrigation systems. This is rapidly changing as codes are updated and modified. For indoor applications, some states require the water to be disinfected even for non-potable uses inside an occupied facility. That includes use for toilet flushing, as well as outdoor cooling tower make-up. This is primarily due to the potential of human contact with the rainwater.
Many states require treatments to control microbial growth and to prevent minerals from clogging plumbing fixtures. Rainwater systems will have a series of filters to reduce the presence of suspended material in the water. After filtering, rainwater can be disinfected by exposure to ultraviolet light, carbon charcoal filters, boiling or chemical treatments such as with chlorine or iodine. Ultraviolet disinfection sterilizes water and kills microorganisms that may be present in the water in enclosed, sealed pressurized units. Although sunlight has ultraviolet rays, it must be prevented from entering storage tanks because of potential algae growth and contamination.
The American Rainwater Catchment Systems Association (ARCSA) is a professional organization that is a source for detailed information on worldwide treatment options. ARCSA's mission is to promote sustainable rainwater harvesting practices to help solve potable, non-potable, stormwater and energy challenges throughout the world.10 ARCSA also provides resources, research, education and professional certifications and training.
|Dwindling Water Resources
and National Security
Sandia National Laboratory is a government research facility located in New Mexico and California. Researchers at Sandia provide information for national security initiatives for the U.S. Department of Energy's National Nuclear Security Administration. The division of Energy, Climate & Infrastructure Security is currently focusing on the potential of a looming water crisis. According to researchers in the Water in the Western and Texas Interconnects study: "water and energy are co-dependent. Water is used directly in hydroelectric power generation and is used extensively for thermoelectric power plant cooling and air emissions control. Water is also needed for energy-resource extraction, refining and processing. Altogether, the energy sector accounts for approximately 41 percent of daily fresh water withdrawals and 49 percent of total overall daily water withdrawals in the U.S. Likewise, significant energy is expended to extract, convey, treat and deliver water and wastewater."13 According to a report published in December 2010, oil companies used 83 percent of California's Central Valley district water for oil extraction. It can take up to eight barrels of fresh water to extract one barrel of oil for shallow oil extraction.14
One of the missions of this ongoing study is to deliver an integrated "Energy-Water Decision Support System" that can be used by planners to analyze the potential implications of water scarcity and evaluate future policies for water transmission and resource conservation. This regional analysis of the energy-water relationship is a coordinated initiative by federal and state agencies, the power industry, non-governmental organizations (NGOs) and other stakeholders. Studies like this initiative will influence future local, state and federal water policies in the future as the country works to balance the need for drinking water with other water intensive uses.
Return on Investment and Celebrating Rainwater
A study from Australia funded by the United Nations Economic and Social Commission for Asia and The Pacific compared the safety of water from city water supplies with the decentralized capture of rainwater from roofs. Concerned about climate change, researchers reviewed opportunities for a "more resilient urban water supply." The study concluded: "urban water strategies should also consider the synergistic benefits of combined strategies (such as water supply from rainwater harvesting and from dams) which include improved reliability of urban water supplies and the potential to buffer the impacts of expected climate change."11
The researchers proposed an eco-efficient delivery of water in the urban infrastructure and a systems approach that minimized costs and environmental impacts across multiple scales. This required a hierarchy of water management beginning at the local scale or source and finishing at the regional scale as a last resort. This approach is dependent on meeting multiple objectives for water security, economics, well-being and protection of the environment at a range of scales.12 Experts continue to find challenges for water management, particularly in light of the 2010 flooding in Queensland, Australia that followed a severe drought in other parts of the country.
One of the most commonly asked questions by owners considering investing in a rainwater harvesting system is what is the return on the investment? Financial return is often based on the offset of the cost of municipal water. In smaller residential systems, the payback in dollars may not equal the investment over time but in larger commercial buildings, the payback can be substantial. In addition to economic benefits, owners are deciding to choose to conserve water to achieve green building certification, to have greater control of their water supply or just wanting to "do the right thing."
Another way to look at the ROI for rainwater capture is to incorporate the tax benefits for consumers. Stormwater management can mean the construction and repair of drainage systems and treatment plants and add to the tax burden of the entire community. Some cities provide tax incentives as well as a reduction in utility rates for the construction of rainwater systems. Individuals and businesses will find savings in their utility bills, have greater control of water availability and find a source of high quality irrigation water without tapping into community water systems. Georgia, Maryland, Texas, Virginia and Hawaii are states that provide rainwater manuals and design resources. Rainwater harvesting is a common sense method to preserve water. Design for rainwater harvesting protects water quality, prevents stormwater runoff, reduces groundwater withdrawal from underground aquifers and conserves valuable drinking water resources.
|9||C. Evans, P. Coombes, H. Dunstan, T. Harrison, A. Martin and A. Morrow. "Rainwater tanks and microbial water quality: Are the indications clear? School of Environmental and Life Sciences, University of Newcastle, NSW.|
|11||Coombes, PJ. and Barry, ME. "The relative efficiency of water supply catchments and rainwater tanks in cities subject to variable climate and the potential for climate change." Bonacci Water, Melbourne, Victoria School of Chemical and Bimolecular Engineering, Melbourne University, Victoria School of Environment and Life Sciences, University of Newcastle, NSW and BMT WBM, Brisbane, Queensland.|
|Founded in 2003, Oakboro, NC-based BRAE is a leading provider of configurable rainharvesting systems and related technology for residential and commercial applications. Using collected water for flushing toilets, irrigating lawns and watering gardens can reduce water consumption by up to 65% in homes and buildings. BRAE is an active participant in the rainwater community and assists customers in adopting this technology for their applications.Â www.braewater.com|