Alternative water sources typically require some form of treatment to remove contaminants from the water, depending on the application that will consume the water. Generally, water treatment includes filtration to physically separate solids and disinfection to kill bacteria and other biological contaminants. The level of treatment can produce water that is either non-potable (cannot be consumed by humans) or potable (safe for human consumption).
This page provides general information on non-potable and potable water and an overview of the Safe Drinking Water Act (SDWA), which can help federal agencies decide what level of treatment is necessary for the intended application of their alternative water sources.
Water at this treatment level has not been treated to standards safe for human consumption, but is useful for specific end uses such as irrigation, dust suppression, toilet and urinal flushing, or make-up water for mechanical equipment.
There are several classifications of non-potable water based on the end use and expected level of human exposure. Categories that address water reuse with unrestricted public exposure are classified as "unrestricted urban reuse," which is typically designated for irrigating public access areas such as residences and parks, and "unrestricted recreational reuse," for recreational activities where public exposure is likely and could entail whole body contact. To be classified in either of these categories, water requires additional treatment. This can be interpreted as a high-quality, non-potable water.
For an end use with limited public-exposure, such as urban irrigation with limited public access, "restricted urban reuse" applies. "Restricted recreational reuse" applies when concerned with non-contact recreation such as boating or fishing watersports. These can be considered lower-quality, non-potable water.
- U.S. Environmental Protection Agency (EPA) 2012 Guidelines for Water Reuse: Provides details and specifications on classifications of water types and treatment options.
- EPA WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities: Provides information about water quality considerations for onsite alternative water sources (see Tables 8-1 and 8-2).
- National Sanitation Foundation (NSF) Standard NSF/ANSI 350 and 350-1—Onsite Residential and Commercial Reuse Treatment Systems: Establishes the minimum requirements for the materials, design, and performance of non-potable onsite reuse systems.
Primary standards are put in place by SDWA and enforced by EPA. These standards require that contaminants within drinking water do not surpass regulatory levels in PWS. Common examples of contaminants that are within the primary standard category are arsenic, chlorine, chlorite, copper, fluoride, lead, and mercury.
Potable water is of sufficient quality for human consumption and is classified, permitted, and approved for human consumption. With proper treatment, it is possible to produce potable water from any alternative water source.
Potable alternative water systems need to produce reliable potable water that meets SDWA requirements. The SDWA is administered by EPA and establishes standards to ensure the safety of public water systems (PWS). A PWS is considered a system that serves at least 25 people or 15 service connections.
A certified operator is required for each PWS to ensure the potable water system is running properly and following SDWA standards. For each PWS, a certified operator is required to perform maintenance on that system and has the authority to make decisions about water quality and quantity. The requirements to become a certified operator vary by state but the basic characteristics include:
- Education: Most states require at least a high school diploma or general education diploma
- Experience: Some on-the-job experience, set by the state
- Examination: Pass a certification test that covers mandatory capabilities and decision-making skills.
In addition to certified operators, the PWS should have certified laboratories test water quality and report their results. The laboratories will test samples for contaminant type and level to demonstrate the compliance with both primary and secondary standards.
Secondary standards are not enforced by EPA but are guidelines provided to help PWS improve their water quality. Contaminants within secondary standards may change the water aesthetically (smell, look, taste) or technically (damage water equipment) but do not pose a significant health risk to the public (such as aluminum, manganese, sulfate, and zinc).
Other best practices of the PWS operators should be to comply with EPA standards, including the following:
- Apply treatment technologies that allow for regulated contaminant levels to be achieved.
- Keep updated on the Contaminant Candidate List (CCL) to be educated on what contaminants are being monitored and may be regulated in the future. (The CCL is a list of contaminants that may be found in a PWS but are currently not regulated by EPA. See the current EPA CCL.
- Maintain disinfecting protocols to ensure that water is treated properly and that the process does not exceed regulation levels.
Water sources that will be used in potable water end uses must be tested regularly for water quality. If it is determined that contaminant levels exceed EPA allowable levels – which will likely be the case for most alternative water sources – it is essential that the water be treated. Treatment technologies should be evaluated by a subject matter expert to determine the proper treatment required to ensure the water is safely treated for the quantity needed.
PWS operators are also required to disinfect water to ensure that any biological contaminants are eliminated. The EPA regulates disinfectants by setting a maximum residual disinfectant level (MRDL), meaning any chemical remaining as a result of disinfection must not exceed its MRDL within drinking water. The MRDL differs among the most common disinfecting chemicals –chloramine, chlorine, and chlorine dioxide, to name a few.
- EPA Safe Drinking Water Act: Establishes the standards for drinking water quality and implements programs to ensure drinking water safety.
- WateReuse—Framework for Direct Potable Reuse: Provides an overview of direct potable reuse and guidance on a direct potable reuse program.
- WateReuse—How Reuse Works: Provides video overviews of different water treatment processes.