Science textbooks tell us that only 3% of the water in the world is fresh water and less than one-third of this amount is available for human consumption. The rest lies either in the polar ice caps, glaciers or deep within the earth. With world population continuing to soar, global water consumption is increasing at a comparable rate. As we look to the future, many are predicting that the major world crisis we will face in the next 50 years will not be an energy crisis, but a global shortage of water, one of life's critical components.
Residents and water utility companies in the western and southern states have realized for years that water is our most valuable resource. The planning for future production and conservation of potable water today is critical to our being able to provide sufficient supplies to meet future needs. In recent years, with populations exploding in the western and southeastern regions of the United States, some areas have experienced inadequate rainfall to provide sufficient surface water for potable supplies. In addition, many states in the region have begun to feel the effects of record droughts, and, as a result, have taken steps to enact water conservation measures.
Traditional methods of addressing water conservation include encouraging water consumers be less wasteful of water by installing low volume fixtures, turning the faucet off while brushing teeth or washing hands, and generally to be more aware of water use. A more aggressive approach to water conservation involves augmentation of the water supply with waters that have historically been disposed of after one use. This approach can take several forms, including the use of graywater systems and reclaimed water systems.
When we speak of “graywater” or “reclaimed water,” we actually are describing the difference in the collection of the water after its initial use. Whatever the source, these types of water have traditionally been used for irrigation purposes or for flushing toilets. These uses are normally defined and regulated by local codes. Homeowners and contractors are generally directed to their local codes office to investigate the applicable uses of reclaimed or graywater in their areas.
We will refer to “graywater” as wastewater that is generated inside a home or business from hand washing, showers, baths, laundry and light cleaning uses. Water from these uses can be collected through a separate sewer system installation, stored onsite and treated for further uses such as toilet flushing or irrigation. In its simplest form, a graywater system consists of separate gravity pipes leading from the drains in the shower or tub, sinks and clothes washing machine to a holding tank in the basement of the dwelling. In order for the water to be used again, it must be cleaned of larger particles and kept from decomposing before reuse. Filters and UV light or chemical disinfection can condition the water before a pump delivers the water on demand through a dedicated supply line to a toilet tank. The water also may be pumped from the storage tank outside to an irrigation system.
Graywater must be cleaned of debris and disinfected to eliminate growth of materials that might clog supply and irrigation lines. It is important to balance the storage requirement with the supply of wastewater and its intended use. If the tank can store more water than can be used in one or two days, then the system must disinfect for a longer period, and the homeowner will incur costs associated with the chemical or UV processes. If a system can be balanced so that the water that is collected can be used within a few hours, then the disinfection costs will be held to a minimum.
Some newly emerging technologies are presently being offered to consumers as packaged systems. These package-type systems are becoming more commonplace in dry areas of the country as homeowners seek ways to conserve water. Although local codes may prohibit such systems, local water utilities may provide supporting information to regulatory bodies to initiate acceptance of these measures to conserve water.
“Reclaimed water” is defined as treated municipal wastewater from various sources that has been processed through a municipal wastewater treatment plant (WWTP) and treated to a high level. Historically, the treated effluent from a WWTP is disposed of by discharging to a nearby stream. Reclaimed water systems make use of this resource by distributing the highly treated wastewater through a distribution network for non-potable use. Reclaimed water has been used successfully for irrigation, industrial process water, impoundments such as fountains, and indoor urinal and toilet flushing.
Historically, the most common use of reclaimed water has been on golf courses. Many golf courses dig wells for irrigation purposes, or they pump water from adjacent streams to fill their lakes and irrigate. When dry periods occur, well production can drop, and streams may no longer provide sufficient flow. The reclaimed water system can provide water to its customers regardless of the weather. As long as there is wastewater being generated and treated at the WWTP, there will be effluent to distribute to reclaimed water customers.
Reclaimed water is often piped through a municipality and into residential neighborhoods through distribution systems composed of purple pipe. The pipe, usually PVC, is colored purple to differentiate it from potable water lines. This helps prevent contractors from mistakenly tapping a reclaimed water main for a potable water service connection. Graywater systems are sometimes injected with a purple dye to color the water so that a colored discharge from a faucet would alert a homeowner not to drink it. These color-coded precautions are an attempt to eliminate cross-connections between the potable water system and reclaimed water systems.
Other methods of distinguishing reclaimed water from potable water system components include the use of valves that open in the opposite direction from a utility's potable water valves. Valve boxes and meter boxes for reclaimed water service are many times cast with the words “reclaimed water” on the lids. The use of purple epoxy paint on system components designates their use as reclaimed water. Imprinting “Caution Reclaimed Water - Do Not Drink” on distribution piping has been customary in some areas of the country in addition to the purple coloring.
Many utilities design their reclaimed water systems to operate at pressures below that of their potable water systems. This safeguard helps to ensure that, in the unlikely event of a cross-connection, reclaimed water will not flow into a potable system. The use of backflow preventers at potable service connections also assists the utility in ensuring segregation of waters. Minimum separations between reclaimed water lines, sewer collection lines and potable distribution lines are customary for utilities that offer reclaimed water.
Water reuse is growing in the United States. Today 1.7 billion gallons of water are reused in the U.S., according to the Water Reuse Association, and it is growing at a rate of approximately 15% per year. At least 27 states currently have water reclamation facilities. We would encourage installers to visit their local code offices to ask if graywater systems are allowed and to inquire with the local utility whether reclaimed water is presently offered to the public.
Bo Butler is vice president at the engineering design and facility consulting firm of Smith Seckman Reid, where he also is a team leader on the civil infrastructure team, Additional information is available at www.ssr-inc.com