Overseas Experiences

Reuse of Treated Used Water is Not New

Unplanned Indirect Potable Use

Planned Indirect Potable Use

The reuse of treated used water is not new. In countries with long riverine systems, upstream communities use the water and discharge the used water after treatment back into the river. Successive downstream communities then reuse the water several times, before the river finally flows into the sea. Until recently, the constraint to greater recycling was cost. This is falling rapidly. New technology is producing superior filters and membranes, and this is significantly reducing the cost of microfiltration and reverse osmosis. It has become economically attractive to recycle used water on a large scale.

Unplanned Indirect Potable Use

Unplanned Indirect Potable Use occurs when a water supply is abstracted for potable purposes from a natural source (surface or groundwater) that is fed in part by the discharge/disposal of treated or non-treated. The subsequent potable use of the wastewater was not an intentional part of the effluent disposal plan. As shown in the figure, this type of potable use occurs whenever an upstream water user (City A) discharges wastewater into a water source (river, lake or aquifer) that serves as a water supply for a downstream user (City B). Many large communities unintentionally have been practising unplanned Indirect Potable Use. Some examples are cities along the Rhine and Thames rivers in Europe, Mississippi River in the U.S., Yangtze River in China, and Mekong River in Indo-China.

Planned Indirect Potable Use is the abstraction, treatment, and distribution of water for drinking from a natural source water (river, lake or aquifer) that is intentionally and partially fed by the discharge of treated wastewater effluent. This type of potable use is becoming more common as other viable water sources have become more scarce because of population growth and watershed urbanisation. Some U.S. examples are Water Factory 21, Orange County Water District, Southern California and Upper Occoquan Sewage Authority (UOSA), North Virginia.