As long as water remains inexpensive and plentiful, water reuse is not a high priority activity for water management. As water becomes more expensive, reclamation and reuse activities gain prominence as an alternative to increasing supplies. In fact, the reclamation and reuse of municipal wastewater is a well-established practice in many areas of the world, and these activities will continue to increase.
In many ways, nature's hydrologic cycle provides an excellent model of water reuse and recycling for water managers. For billions of years the Earth has naturally "reused" water through its hydrologic cycle, which continuously cycles water from the sea, to air and land, and back to the sea. * Almost every drop of water that falls on land eventually returns to the oceans. There is as much water on Earth today as there ever was—or ever will be. Thus, every glass of water consumed contains water molecules that have been used countless times before. In this way, all water on Earth can be seen as being reused again and again.
Water entering the reuse cycle begins its journey either in potable (drinkable) form or in nonpotable (not drinkable) form. Applied mainly to municipal water supplies, the technologies and processes designed to facilitate each type of water reuse is distinct.
In direct potable reuse, the liquid waste or sewage of a wastewater treatment plant is sent directly into the intake of a drinking-water treatment and distribution plant. Although this process involves the most technologically advanced water treatment processes, and the water that enters the distribution system must meet drinking-water standards, it is the one most argued against by community citizen groups, calling it "toilet-to-tap". It is presently used only in water-critical situations, such as those that frequently occur in drought areas.
Indirect potable reuse is the addition to a water supply of reclaimed water derived from pretreated municipal wastewater. This often is done through the medium of an existing stream or river and, as a result, the wastewater generally is diluted significantly. Many communities use this method inadvertently because their drinking-water intake lies downstream of the collective discharges of other municipalities' wastewater plants. Indirect potable reuse also is called nonpotable reuse because the technologies used for each are the same.
The main technology involving groundwater is reservoir infiltration, in which an aquifer is supplemented with treated wastewater infiltrating from a surface basin. The injection of reclaimed wastewater also is used in
Direct nonpotable reuse is the immediate addition of reclaimed water to a water distribution system. It uses a similar level of treatment as traditional wastewater prior to discharge into bodies of water. The technology involved usually is an additional set of water pipes (alongside drinking-water pipes) that carry treated wastewater back to large irrigation sources, such as city gardens, golf courses, and industrial or municipal parks.
The Earth's natural supply of water is not evenly distributed. Some regions enjoy abundant water resources, whereas others—in arid regions, for example—struggle to find adequate supplies for their often-growing populations. This variation in water availability has led to different patterns in both the use of water and the rates of efficiency with which water is used. In general, the more abundant and inexpensive that water supplies are, the less incentive there is to use water wisely.
As water supplies and water-use efficiency rates vary widely around the world, reclamation and reuse are increasingly important activities for water managers in many areas. Doing more with less water essentially creates a new source of supply, without having to build a new reservoir or deplete groundwater. Each liter of water conserved or reused is a liter that need not be taken from the hydrologic cycle. Using water resources more efficiently reduces water demand and makes water supplies available for other uses, such as instream flows.
Increasing water scarcity and diminishing prospects for creating new water supplies place attention on increasing the efficiency with which water is used for agricultural and municipal uses. Particularly in the United States, it is increasingly difficult to fund large water-supply projects or to find locations suitable for such projects. Thus, water management programs are transitioning from dam-building, drilling, and diverting activities to improving
The word "reclamation" has a long history in water resources management. In 1902, the U.S. Congress passed the first National Reclamation Act that created the Bureau of Reclamation and authorized it to construct irrigation projects in the western states and territories. The Bureau was to reclaim the arid West by providing water vital for land development; today the Bureau is a major manager of the West's water resources.
Modern usage of the term "reclamation" refers to projects that reclaim usable water from wastewaters: that is, to take the waste component out of wastewater and reclaim the water for beneficial uses such as irrigating pasturelands and augmenting potable water supplies. The use of reclaimed water is most significant and cost-effective near urban areas where large volumes of wastewaters are generated.
Reclamation views wastewater as a resource to be put to productive use, rather than as a waste to be disposed of. Water reclamation refers to the treatment of wastewater to produce reclaimed water. Developed nations commonly use water of drinking-level quality to water lawns, flush human waste into sewers, and so on. Many water uses do not require water of such high quality, and therefore important opportunities exist to put reclaimed water of lesser qualities to productive uses.
Water recycling refers to using water more than once by the same user; for example, in a home or factory. Water reuse refers to using water more than once after it is reclaimed and redistributed to a new use, such as from municipalities to farms. Water reuse often requires some level of treatment, but not necessarily to the highest standards for drinking water. The level of treatment required depends on the potential level of human contact or ingestion associated with the reuse activity.
The adoption of water reclamation and reuse programs depends on the costs and benefits of such a program. Areas facing limited water availabilities and high costs of developing new supplies frequently turn to reclaimed water as a potential source of water. Uses for reclaimed water range from landscape irrigation and snowmaking to groundwater recharge and crop irrigation.
The idea of applying wastewater to cropland is not a new one. Scottish "sewage farms" were operating in the 1650s and the practice spread to other English cities. Today over 500,000 hectares (1,930 square miles) in fifteen countries are irrigated with municipal wastewaters. Australia's Werribbee Farm, in operation since 1897, is one of the largest reclaimed wastewater operations utilizing a system of wastewater ponds.
Israel currently has the most advanced wastewater reuse system in the world. Approximately 70 percent of the country's wastewaters are treated and reused to irrigate 19,000 hectares (73 square miles) of agricultural land. Israel reuses municipal wastewaters by using ponds and reservoirs to biologically treat sewage, making it safe for watering crops that will not be eaten raw. Israel also treats sewage and uses it to recharge groundwater basins, where it is further treated and then pumped and piped to farms for irrigation.
The practice of using treated wastewater to irrigate cropland originally fell out of favor due to concerns over health issues, especially those by bacteria, viruses, and parasitic worms. Current knowledge is enabling advancements in safe agricultural water reuse, and the World Health Organization has set standards for treating wastewater for irrigation of crops not eaten raw. In the United States, the Environmental Protection Agency set some guidelines for water reuse in 1992, but there are no federal standards or regulations governing water reuse. Not all states have regulations on water reuse, but many have looked to California's standards as a model to follow.
While most wastewater constituents are viewed as pollutants , some constituents are nutrients that belong on the land where they originated. Wastewaters contain large amounts of nitrogen, phosphorous, and potassium. Using water twice—once for municipal use and once for irrigation use—converts would-be pollutants into valuable fertilizers while protecting rivers and lakes from contamination and providing a local source of water supply. Studies have shown that using treated wastewaters can decrease the need for expensive chemical fertilizers, and many crops can do well with no further chemical or organic fertilizer.
Making reclaimed water suitable for reuse applications is done by eliminating or reducing the concentrations of pathogenic (disease-causing) microorganisms and chemical constituents through some type of wastewater treatment. While standards typically address limits on fecal coliforms and parasitic worms, care must also be taken to prevent damaging levels of heavy metals from getting into wastewater streams. Municipal wastewaters that are influenced by industrial effluents can pose a problem for irrigation use. Cadmium, copper, nickel, zinc, and other heavy metals tend to accumulate in soil and crops, and can also percolate into and contaminate groundwater. Thus a key to safe reuse is preventing industrial effluent from mixing with domestic-use wastewaters.
Irrigation reclamation and reuse practices in some developing countries do not meet World Health Organization standards. In several areas, wastewaters from municipal sources receive no treatment before being used for irrigation, and often are applied even to crops typically eaten raw. Some vegetables are then highly contaminated with fecal coliforms and pose a health threat. In South America, several typhoid fever outbreaks have been related to the practice of applying raw sewage for irrigation. These unsafe irrigation practices highlight the need for reclamation and reuse activities to be part of overall water planning and management processes.
Many cities have integrated reuse plans into their water management strategies. In addition to sending reclaimed waters to farms for irrigation purposes, cities themselves reuse wastewater to irrigate parks, playgrounds, greenbelts, cemeteries, and golf courses, and for other nonpotable uses such as toilet flushing, fire protection, street cleaning, and fountains.
In the United States, cities located in water-stressed regions are on the cutting edge of water-reuse activities. For example, Los Angeles has set the goal of reusing 40 percent of its municipal wastewaters within 20 years. This goal is an important component of plans to recharge underlying aquifers and combat seawater intrusion into their coastal groundwater reserves. Arizona also has ambitious water reuse plans calling for 19 percent of all water needs to be met through reclaimed wastewater.
Only one major U.S. city, St. Petersburg, Florida, completely reuses all of its wastewater and discharges none to its surrounding lakes and rivers. The city has developed dual water distribution systems—one for delivering drinking-quality water and one for delivering treated wastewater. The treated water costs about one-third less than the drinking-quality water.
Only a few cities around the world add reclaimed wastewater to their public supply. Windhoek, Namibia was the first to do so (in the late 1960s). Although this is not currently practiced in the United States, studies are being conducted on the feasibility of reclaiming wastewater to drinkingquality and on injecting highly treated wastewater into aquifers that will eventually reach public water supplies. For example, the city of Denver studied direct potable reuse for over 10 years at a cost of $50 million, and concluded it was not yet feasible.
In general, converting wastewater into drinking-quality water makes less economic sense than converting it into irrigation water, due to the relatively high cost of treatment required to meet drinking-water standards. Moreover, the largest obstacle to reusing wastewater may be psychological; in other words, the public may struggle to accept this practice as good water management that safeguards their health and well-being.
Water reuse supports the recycling ethic that many communities have embraced enthusiastically. Few people think twice about recycling aluminum cans or milk jugs. But reclaimed wastewater presents a different picture for many people, particularly when the subject of reclaiming wastewater for potable purposes is discussed. The extent to which water reuse is accepted depends on several factors, including perceptions on the safety of reclaimed water, the uses it will be put towards, and how closely those uses appear to affect users. For these reasons, testing and monitoring often are integral aspects of reclamation programs.
Water is used in many industrial processes, for cooling, washing, and incorporation into products. Industry accounts for almost a quarter of worldwide water use, and this figure will increase as economic development advances. In the more advanced economies, industry accounts for between 50 and 80 percent of total water demand. Most of this water is used for activities that heat or pollute water, but that do not consume it the way irrigation does. Thus, much potential exists for recycling and reusing industrial water. More than 40 percent of reclaimed water in Japan goes to meet industrial water use needs. In California, only 6 percent is applied to industrial uses.
Typical industrial uses of reclaimed water might include cooling, boiler feed, stack scrubbing, and process water. The quality of the reclaimed water needed for industrial purposes greatly depends on the specific industry and its product. For example, the use of reclaimed water in the paper and pulp industry is a function of the quality of the paper being produced. The higher the grade of paper, the greater its sensitivity to the quality of the water used to produce it.
Several areas are using reclaimed water for environmental uses, such as stream augmentation, and for wetlands , marshes, and fisheries. The required level of treatment increases as the potential for human contact increases. Reclaimed water has also been used to recharge potable groundwater aquifers. For example, Los Angeles County has helped recharge its aquifer by surface-spreading of reclaimed water since 1962, and approximately 30 percent of the inflow to the basin is from reclaimed water. Fiveyear health studies show no adverse effect on the quality of the groundwater or on the health of the population ingesting it, although some concerns remain over the long-term impacts from any potential chemicals.
A few groundwater recharge projects in the United States have involved direct injection of reclaimed waters into aquifers. For example, Orange County, California uses direct injection of reclaimed water to help form a barrier to sea-water intrusion. The city of El Paso, Texas uses direct injection to its underground aquifer with the goal of eventually providing 25 percent of future water needs with reclaimed water. Several municipalities also have used reclaimed waters to augment surface-water supplies. For example, a water reclamation plant in Virginia discharges reclaimed water into the Bull Run River, 32 kilometers (20 miles) upstream of the water-supply intake.
High-quality supplies of water can be created by the careful treatment of wastewater. Reclaimed water is now valued as a resource. By tailoring the quality of water supplies to the needs of the use to which they will be applied, water managers can create more value from each liter of water removed from a river, lake, or aquifer. At the same time, reuse lessens the pressures to develop new sources of water supplies.
Potentially the greatest gains will come from reusing wastewater on a large scale for irrigation purposes, given the vast amount of water diverted for agriculture worldwide. To achieve these potential benefits from reclamation and reuse for society, water managers must ensure safe and sanitary practices for wastewaters moving to other uses.
SEE ALSO Artificial Recharge ; Conservation, Water ; Hydrologic Cycle ; Population and Water Resources ; Rainwater Harvesting ; Supply Development ; Uses of Water ; Wastewater Treatment and Management.
and William Arthur Atkins
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Greywater is defined as the wastewater produced from anywhere in the home except in toilets, urinals, and any drains equipped with garbage disposals. (The wastewater generated by toilets is called blackwater.) Dishwashers, showers and bathtubs, bathroom and kitchen sinks, and washing machines are common sources that produce greywater. These items make up the majority of household wastewater.
Greywater systems are modifications of septic system technology. The primary modification is the location of the drainfield, which is in the root zone of plants. This makes greywater useful as irrigation. An important feature of a greywater system is the isolation of blackwater to a separate system, leaving greywater available for reuse.
* See "Hydrologic Cycle" for an illustration of the water cycle.