The Potential of Greywater Systems to Aid Sustainable Water Management
As pressures on freshwater resources grow around the world and as new sources of supply
become increasingly scarce, expensive, or politically controversial, efforts are underway to
identify new ways of meeting water needs.
Greywater is distinguished from more heavily contaminated “black water” from toilets. In many utility systems around the world, greywater is combined with black water in a single domestic wastewater stream. Yet greywater can be of far higher quality than black water because of its low level of contamination and higher potential for reuse.
When greywater is reused either onsite or nearby, it has the potential to reduce the demand for new water supply, reduce the energy and carbon footprint of water services, and meet a wide range of social and economic needs.
In particular, the reuse of greywater can help reduce demand for more costly high-quality potable water.
A greywater system, on the other hand, captures water that has been used for some purpose, but has not come into contact with high levels of contamination, e.g., sewage or food waste. This
water can be reused in a variety of ways. For instance, water that has been used once in a shower, clothes washing machine, or bathroom sink can be diverted outdoors for irrigation.
There are pilot greywater systems that divert greywater from showers and sinks into treatment wetlands or other plant- and soil-based filters. For example, in Berlin, Germany, a 60 square meter engineered wetland constructed in the courtyard of a housing settlement has been operating successfully for eight years (Nolde Grey Water Recycling).
Greywater from bath tubs, showers, sinks, and washing machines enters the plant-covered soil filter where it undergoes biological treatment. Ultra violet disinfection has been included as a final safety measure before the use in toilet flushing (Deutsche BauBeCon, 1995, 1996). Extensive investigations over several years of operation have shown that within the soil filter, E. coli concentrations were reduced by over 99% and all hygiene requirements have been achieved under the EU-Guidelines for Bathing Waters.