Reclaimed water, often called recycled water or water reuse, is wastewater that has been treated and purified to a quality suitable for beneficial purposes. This process transforms a community’s used water, such as municipal sewage or industrial discharge, into a reliable, locally controlled resource. As populations grow and climate patterns shift, water reclamation has become a strategy for sustainable water management. The technology ensures this purified water meets stringent quality standards specific to its intended application, ranging from irrigation to supplementing drinking water supplies.
What Reclaimed Water Is
The source material for reclaimed water is typically municipal wastewater, including sewage from homes and businesses. This water is collected and sent to a treatment facility, where it undergoes a series of cleansing steps. The terms “reclaimed water” and “recycled water” are often used interchangeably, referring to water treated for reuse before it returns to the natural water cycle.
Reclaimed water is distinct from potable water, which is treated to meet drinking water standards, and stormwater, which is runoff from rain or snowmelt. Potable water is held to the highest standard for human consumption, but reclaimed water is treated only to a level appropriate for its secondary use. This approach conserves finite freshwater resources by utilizing a supply that would otherwise be discharged.
The Multi-Stage Purification Process
The transformation of wastewater into reclaimed water involves a progression of physical, biological, and chemical treatment stages. The initial step is primary treatment, a physical process where large debris, grit, and solids are removed from the incoming wastewater through screens and sedimentation tanks. This prepares the water for subsequent, more intensive cleaning processes.
Following the removal of solids, the water moves to secondary treatment, which is largely a biological process. In aeration tanks, naturally occurring microorganisms, such as bacteria, consume the dissolved organic material remaining in the water. Air is bubbled through the water to supply the oxygen necessary for these microbes to break down the organic contaminants.
The next phase is tertiary treatment, which focuses on filtration and disinfection to remove remaining suspended solids and pathogens. Filtration typically involves passing the water through fine granular material or specialized membrane filters to block microscopic particles. This is followed by disinfection, often using chlorine or ultraviolet (UV) light, to inactivate bacteria, viruses, or other disease-causing organisms.
For the highest-purity applications, an advanced treatment stage is added. This stage commonly employs technologies like microfiltration, followed by reverse osmosis (RO) and advanced oxidation. Reverse osmosis forces the water under high pressure through extremely fine membranes that strip out dissolved salts, pharmaceuticals, and trace organic compounds, producing water of near-distilled quality.
How Reclaimed Water Is Used
The degree of purification directly determines the applications for which reclaimed water is safe to use. Most reclaimed water is used for non-potable purposes, meaning it is not intended for drinking. Common non-potable applications include the irrigation of landscaping, such as golf courses, public parks, and agricultural fields for non-food crops.
Industrial users rely on reclaimed water for processes like cooling towers in power plants and boiler feed water, which require large volumes of water. Within urban areas, highly treated reclaimed water is increasingly used for toilet flushing and fire suppression systems in commercial and residential buildings. This substitution helps reduce the strain on local drinking water supplies.
For potable reuse—where the water is eventually consumed—treatment is taken to the highest standard. Indirect potable reuse (IPR) involves blending the purified water with a natural water source, such as an underground aquifer or a surface reservoir, for an environmental buffer before it is withdrawn and treated again for drinking.
In contrast, direct potable reuse (DPR) involves purifying the water to drinking water quality and then introducing it directly into the public water supply system or a drinking water treatment plant without an environmental intermediary. Both IPR and DPR require multi-barrier advanced purification to ensure the water quality meets or exceeds federal and state drinking water standards.
Regulatory Oversight and Safety Standards
The safety of reclaimed water is ensured through stringent regulatory frameworks and continuous monitoring. While the U.S. Environmental Protection Agency (EPA) provides national guidelines for water reuse, the permitting and establishment of water quality standards are primarily managed at the state level. These state regulations specify the level of treatment required for each intended use, such as California’s Title 22 standards for non-potable use.
Water reclamation facilities must perform rigorous, continuous testing to confirm the water quality meets established standards for pathogens and chemical constituents. This testing regime often involves monitoring parameters more frequently than is required for conventional drinking water sources. The safety process relies on a multi-barrier approach, where a failure in one treatment step is compensated for by the redundancy of subsequent purification stages.
To prevent cross-contamination with the drinking water supply, separate distribution systems are required for non-potable reclaimed water. This infrastructure is often distinguished by dedicated piping, frequently colored purple, which alerts utility workers and the public that the water is not intended for consumption. State and local health agencies conduct regular inspections and audits to ensure all operational and infrastructure requirements are met.