Under the Safe Drinking Water Act (SDWA), EPA sets standards for approximately 90 contaminants in drinking water including bacteria and disinfection by products. For each of these contaminants, EPA sets a legal limit, called a maximum contaminant level. EPA also sets secondary standards for less hazardous substances based on aesthetic characteristics of taste, smell and appearance, which public water systems and states can choose to adopt or not. Though 90 contaminants is a lot, there are approximately 80,000 chemicals in use in our society and an uncounted number of pathogens.
When EPA looks for emerging contaminants they look at the nation on a statistical basis, so that contaminants emerging from wastewater reuse would be hidden by the vast number regulated water supply companies that are not yet utilizing recycled water; and does not necessarily search for micro traces. EPA requires that all public water supplies be tested for the SDWA list of contaminants on a regular basis and meet these minimum standards, but EPA does not control or regulate the water for the 14% of the population that gets their water from a private well.
As the demand for water grows in our cities and population centers, we are straining to meet the demand. Even in generally water rich areas there are limits to the availability of water and United States has slowly and quietly begun to address the availability of water by recycling the wastewater. In the United States municipal wastewater represents a significant potential source of reclaimed water, an estimated 32 billion gallons of water a day is treated in wastewater treatment plants throughout the country. The National Research Council Water Science & Technology Board estimates that only about 8 % of this municipal waste water is reused, but a third of this water could be reused. (NRC Water Science & Technology Board titled Water Reuse: Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater)
Recycled or reclaimed water is former wastewater (sewage) that has been treated to remove solids and certain impurities, and then is used in irrigation, discharged to surface water that is a source of drinking water or injected into the ground to recharge groundwater aquifers. In order to make our river, lake, stream and ocean water safe for fishing and recreation, the Clean Water Act of 1972 mandated elimination of the discharge of untreated waste from municipal and industrial sources. Modern wastewater treatment plants, usually using sand filtration and chlorination or chloramine in addition to primary and secondary treatment, were required to meet certain standards. These standards were not designed to render the waste water potable.
Direct water recycling is reusing treated wastewater for beneficial purposes such as agricultural and landscape irrigation, industrial processes, toilet flushing, and replenishing a ground water basin (referred to as ground water recharge) and less commonly returning the water directly to reservoirs. In some places the treated wastewater is being returned to the drinking water treatment plant, though many of the existing projects that recycle waste water avoid the negative emotional response of drinking water from wastewater treatment plants by either using the water for municipal irrigation or by treatment and then supplementing river flow, reservoirs or groundwater.
Treated wastewater is increasingly being seen and used as a resource. Water reclamation and reuse have taken on increased importance in the water supply of communities in the United States. Increasingly strict effluent discharge limits have resulted in effective and reliable improvements in wastewater treatment technologies. Along with a growing interest in more sustainable water supplies, these improvements have led an ever increasing number of communities (especially in the arid west and urban centers) to use reclaimed water as an alternative source to conventional water supplies for a range of applications.
In some areas of the United States, water reuse and dual water systems for distribution of reclaimed water for non-potable uses have become fully integrated into local water supplies and will expand to become necessary components of sustainable water management. As recycled and reclaimed water is added to the water supply through direct and indirect means, the potential for impacts to the overall water supply increases. Varying amounts of pathogens, pharmaceutical chemicals (e.g., hormones from female hormonal contraception and other pharmaceuticals in common usage) and other trace chemicals are able to pass through the treatment and filtering process, potentially causing danger to humans by their ubiquitous presence in the water supply.
Recognizing the need to provide national guidance on water reuse regulations and program planning, the EPA has updated their comprehensive, water reuse “guidelines” to support regulations and guidelines developed by states, tribes, and other authorities. Water reclamation and reuse standards in the United States are the responsibility of state and local agencies—there are currently no federal regulations for reuse. This may be appropriate since the method of reuse and natural conditions are entirely local. For example depending on the method and purpose of groundwater recharge, most states require either a minimum of secondary treatment with or without additional filtration for groundwater recharge. State Underground Injection Control programs and Sole Source Aquifer Protection are included under Sections 1422 of the SDWA, which provides safeguards so that aquifer recharge wells do not endanger current and future underground sources of drinking water.
There is currently no specific requirement for nutrient removal, but lower effluent nutrient concentrations required for point source discharges could meet strict nutrient groundwater recharge requirements. Nutrient removal at the wastewater plant is also thought to remove N-nitrosodimethylamine (NDMA) precursors, and may remove other contaminants. We must be especially careful of the quality of water used to recharge groundwater. The potential to introduce trace contaminants into our essential groundwater aquifers justifies extra care and expense to ensure water quality. Water technology has improved to the point that a wide range of treatment options are available such that almost any level of water quality can be achieved with reclaimed water.