BMP #14 - Alternate Water Sources
Background
Many facilities may have water uses that can be met with non-potable water from alternate water sources. There are four major categories of alternative water sources potentially available to facilities: municipal supplied reclaimed water, treated gray water from on-site sanitary sources, Alternate on-site sources of water are most economic to capture if included in the original design. Common uses for these sources include landscape irrigation, ornamental pond and fountain filling, cooling tower makeup, and toilet and urinal flushing. One additional water source category that is not widely used is storm water.
Municipal supplied reclaimed water has been treated and recycled for non-potable use. This water is often available at a significantly lower rate than potable water; however, use of reclaimed water is often restricted by local codes. Sanitary gray water is water that is generated by bathroom sinks, showers, and clothes washing machines and can contain pathogens. Non-sanitary gray water is water generated by industrial processes or equipment such as reverse osmosis reject water and cooling tower condensate and can contain chemicals, minerals, and solids.
Traditionally, centralized municipal sewage treatment facilities have been the primary source of water disposal for government facilities. However, heightened concerns about the availability of our water supply have encouraged facility managers to consider on-site recycling of their wastewater. In a typical gray water recycling system, water that would normally be discharged for municipal sewage treatment is collected, treated to remove suspended solids and contaminants, and reused. On-site wastewater recycling applications are currently found in states with persistent drought conditions. However, all arid, semiarid, and coastal areas that have experienced water shortages, as well as major urban areas where sewage treatment plants are overloaded and expansion is constrained, are potential candidates for on-site recycling. The recycled water is typically used as flush water for toilets and urinals, landscape irrigation, supply water for ornamental ponds, and make-up water for cooling towers.
At its most basic, gray water treatment consists of removing suspended solids from the water. Filtering with no additional treatment may be applicable for rinse water from laundries or car washes and air handler condensate. At its most sophisticated, treatment may consist of biological treatment with membrane filtration, activated carbon, and ultraviolet light or ozone disinfection to destroy pathogens. The basic gray water system will include storage tanks, color-coded piping, filters, pumps, valves, and controls.
Rainwater harvesting captures, diverts, and stores rainwater for later use. Captured rainwater is often used in landscaping, because the water is free of salts and other harmful minerals and does not have to be treated. It is also useful in attracting and providing water for wildlife. Rainwater harvesting can also help to prevent flooding and erosion, turning storm water problems into water supply assets by slowing runoff and allowing it to soak into the ground. Reducing run-off also helps to reduce the contamination of surface water with sediments, fertilizers, and pesticides in rainfall run-off.
Rainwater can be collected in cisterns and used with little or no treatment for a variety of non-potable purposes. The major components of a rainwater harvesting system include the catchment area/roof or surface upon which the rain falls, gutters and downspouts to carry the water to storage, leaf screens to remove debris, cisterns/storage tanks to store the harvested rainwater, conveyances to deliver the stored water either by gravity or pump, and a water treatment system to settle, filter, and disinfect the water, if required.
Like rainwater, storm water can be harvested and reused for washdown, cooling tower make-up or process water, dust suppression, and vehicle washing. Storm water harvesting differs from rainwater harvesting as the runoff is collected from drains or creeks, rather than roofs. The characteristics of storm water harvesting and reuse schemes vary considerably between projects, but most schemes include collection, storage, treatment, and distribution. Storm water is generally collected from a drain, creek, or pond and then stored temporarily in dams or tanks to balance supply and demand. Storages can be on-line (constructed on the creek or drain) or off-line (constructed some distance from the creek or drain). Captured water is typically treated to reduce pathogens and pollution levels through the use of constructed wetlands, sand filters, and disinfection techniques including chlorine, UV radiation and membrane filtration. The degree of treatment required depends on the proposed use, particularly the level of public exposure. Urban storm water harvesting and reuse is a relatively new field of water management and most of the projects constructed to date have been pilot projects in drought areas in Australia and the United States. Successful storm water harvesting and reuse scheme needs specialist input from a number of areas including storm water management, water supply management, environmental management, and public health. The potential limitations and disadvantages to storm water harvesting and reuse schemes include variable rainfall patterns, environmental impacts of storages, potential health risks, and high relative unit costs of treated storm water. Although this is not a practice that would be feasible at many Federal facilities, storm water harvesting and reuse is an emerging practice that may be useful in specific situations.
To develop an efficient and successful reclaimed water project you must have a reliable source of wastewater of adequate quantity and quality to meet your non-potable water needs. These projects are economically more viable when the cost of water is high, there is a lack of high-quality freshwater supply, reuse is the most cost-effective way to dispose of wastewater effluent, and there are local policies that encourage the use of reclaimed water, or water efficiency.
For more information on this and other FEMP Water Efficiency Best Management Practices (BMPs), please see the resources section.
Operation and Maintenance Options
- As described in other BMPs, potential non-potable water use should be identified while reviewing current water use practices. The use of non-potable water is generally most cost-effective when included in the design of new facilities.
- For specifics, consult with experts in the field. Your first resource should be your local or higher headquarters engineers, but do not rule out the benefits of input from experiences from contractors or other Governmental agencies.
- Facilities using alternative on-site water sources must comply with all applicable backflow prevention requirements.
Municipal Supplied Reclaimed Water
- Municipal supplied reclaimed water pipes must be color coded with purple tags or tape according to standards set by the American Water Works Association to minimize cross-connection problems.
- Signs should be used liberally to indicate that reclaimed water is non-potable. Place them in public places such as in front of a fountain and on valves, meters, and fixtures.
- Keep the pressure of reclaimed water to 10 psi lower than potable water mains to prevent backflow and siphonage in case of accidental cross-connection.
- Run reclaimed water mains at least 12 inches lower in elevation than potable water mains, and horizontally at least 5 feet away.
- Review the quality of reclaimed water to ensure there will be no harmful effects, such as salt buildup, from long-term use.
Gray Water Recycling Systems
- The pathogenic organisms in sanitary gray water must not come into contact with either humans or animals. This can be accomplished by treating the water to eliminate pathogens or avoid their introduction into water by not mixing sanitary gray water with any potable water source. Human exposure can be prevented by not collecting or storing it in an open container.
- Sanitary gray water used for irrigation should not be applied directly through a spraying device, but rather injected directly into the soil through drip irrigation. Drip irrigation allows you to receive the benefits of using recycled water and at the same time avoid contaminating animals, humans, and edible plants.
- If you install a gray water recycling system, consider using biodegradable cleaning products that do not contain sodium, chlorine, or boron. Cleaning products that contain high chemical levels may make their way into the gray water recycling system and could poison plants or damage soil through the buildup of inorganic salts.
- Rain or excessive irrigation could cause ground saturation and result in pools of gray water on the surface. To help eliminate this situation, turn off the gray water system and divert the gray water to the sanitary sewer line during rainy periods.
- A maintenance program for a gray water system must include the following steps, all of which must be performed regularly:
- Inspecting the system for leaks and blockages
- Cleaning and replacing the filter bimonthly
- Replacing the disinfectant
- Ensuring that controls operate properly
- Periodically flushing the entire system
Retrofit and Replacement Options
Gray Water Recycling System
- The use of on-site wastewater recycling systems should be considered when constructing new buildings. Even though many of these systems are costly to purchase, the payback period in savings from discharging less wastewater can be as little as 10 years or less.
- Gray water systems must be installed in accordance with local plumbing codes and by professional, licensed plumbing contractors. Installing a gray water system requires the retrofitting of existing plumbing, and all alterations to the plumbing system must be approved by local authorities.
- All counties and cities that permit gray water recycling require building inspections to inspect sites and, after the installation, verify compliance and proper operation of the gray water system.
- Local authorities may require that gray water supply systems be clearly distinguished from potable water supplies. Methods of doing so may include extensive labeling of the system or the use of different piping materials for the different systems. All graywater outlets must be clearly labeled to indicate that they dispense non-potable water. Local codes also may require marking gray water supplies by adding biodegradable dye. Additionally, backflow preventers also must be installed to ensure the proper separation of potable water and gray water supply system.
- For buildings with slab foundations, recoverable gray water may be limited to washing machine discharge, because most drain pipes such as for sinks are buried beneath the slab and thus not easily accessible without a significant additional expense.
- For buildings with perimeter foundations, gray water may be recoverable from most sources due to accessibility to piping from crawl spaces.
- Depending on the gray water source, application, recycling scheme, and economics, one gray water treatment method (e.g., media filtration, collection and settling, biological treatment units, reverse osmosis, sedimentation/filtration, physical/chemical treatment) may be more appropriate than the other.
Rainwater Harvesting
- Rainwater collection and distribution systems can be incorporated into almost any existing site, although it is easier to incorporate them into new construction.
- According to The Texas Manual on Rainwater Harvesting, you can collect 600 gallons of water per inch rain per 1,000 square feet of catchment area. To determine how much water you could collect in a year (1) calculate the roof catchment area, (2) multiply the collection area in square feet by 0.6 gallons per square foot per inch of rain times the collection factor (which measures your collection efficiency; 80 percent or 0.8, would be a good efficiency) times the average rainfall, (3) divide this figure by 365, and that will give you your daily collection figure.
Alternate Water Sources Resources
Some of the following documents are available as Adobe Acrobat PDFs. Download Adobe Reader.
Air Force Civil Engineer Support Agency. Air Force Water Conservation Guidebook, May 2002.
Department of Environment and Conservation NSW Australia. Managing Urban Stormwater: Harvesting and Reuse, ISBN 1 74137 875 3. April 2006. (PDF 937 KB).
General Services Administration. Water Management: A Comprehensive Approach for Facility Managers.
Military Handbook: Water Conservation. MIL-HDBK-1165. April 1997.
New Mexico Office of the State Engineer. A Water Conservation Guide for Commercial, Institutional and Industrial Users, July 1999.
Texas Water Development Board. The Texas Manual on Rainwater Harvesting. 3rd Edition. July 2005. (PDF 15 KB).
U.S. Department of Energy, Technology Focus: Savings Energy, Water, and Money with Efficient Water Treatment Technologies, DOE/EE-0294, June 2004.
US Environmental Protection Agency and Department of Energy. Labs for the 21st Century and Labs for the 21st Century - Best Practices (PDF 474 KB).