Water reuse, often called water recycling or water reclamation, involves treating previously used water to make it suitable for a new, beneficial purpose. This practice transforms municipal wastewater, industrial effluent, or storm runoff into a reliable resource that supplements traditional freshwater supplies. This practice is a globally important strategy for communities facing growing populations and increasing water scarcity, reducing the strain on natural sources like rivers, lakes, and aquifers.
Categorizing Water Reuse
Water recycling is broadly categorized based on the intended final use and the corresponding treatment level required. The most common category is non-potable reuse, where the water is used for purposes other than human consumption. This includes applications such as industrial cooling, toilet flushing in commercial buildings, and landscape irrigation for parks and golf courses.
Potable reuse involves treating water to meet or exceed drinking water standards. Potable systems can be indirect, where the highly treated water is blended with an environmental buffer like a groundwater basin or reservoir before being withdrawn and treated again. Direct potable reuse skips this environmental step, sending purified water directly into a drinking water distribution system or treatment plant.
Example: Reusing Water for Crop Irrigation
One of the largest volume and longest-established examples of planned water reuse is the application of reclaimed municipal wastewater for crop irrigation. This practice is especially widespread in arid and semi-arid regions where agriculture consumes a significant portion of available freshwater. The process begins with municipal sewage, which first undergoes primary treatment to remove large solids and debris. Next, the water moves through secondary biological treatment, where microorganisms consume dissolved organic matter.
For irrigation, the water typically receives advanced treatment (tertiary treatment), involving filtration to remove suspended solids and fine particles. The specific destination dictates the quality standard, often leading to a distinction between crops. Treated wastewater is commonly used to irrigate non-food crops like cotton or hay, or food crops that are processed or peeled before consumption, such as citrus and nuts. The reclaimed water also contains residual nutrients like nitrogen and phosphorus, which can reduce the need for synthetic fertilizers.
Ensuring Water Safety and Quality
The paramount concern in any water reuse scheme is public health, which is managed through a “fit-for-purpose” approach to treatment and regulation. The quality of reclaimed water must meet strict regulatory standards set for its intended end-use. Non-potable reuse requires robust pathogen control, typically achieved through multiple treatment barriers that include filtration followed by a final disinfection step, such as chlorination or ultraviolet light. Regulatory bodies establish minimum log reduction targets (LRTs) for pathogens like viruses and bacteria, ensuring the water presents a minimal public health risk.
To prevent any accidental mixing with the drinking water supply, reclaimed water is delivered through a completely separate piping system, often identified by a distinctive purple color. Continuous monitoring and testing protocols are implemented throughout the system to verify that the water quality consistently meets all required standards before it is released for irrigation.