The water consumed by households must be of a sufficiently good quality to safely drink, bathe and clean with. However, the quality of water required for each of these needs differs significantly. For example, potable or drinking water must be of a higher quality than the water used to flush a toilet or irrigate a garden (so called “greywater”). It is possible to significantly reduce our overall water consumption by using and reusing non-potable water sources for lower quality purposes—a strategy particularly relevant for drought-stressed cities.

Greywater reuse systems can be applied at household level to collect water from showers and baths, filter and treat it, and then recirculate it to flush toilets or irrigate gardens. Alternatively, a sports centre can collect greywater from showers and hand basins and process it to be used to irrigate an adjacent sports field or community garden.

Cities can encourage the uptake of greywater reuse systems through awareness campaigns, regulations and financial incentives. Awareness campaigns can show the potential environmental and financial benefits of installing greywater systems. Regulations can be in the form of building codes and requirements in which the installation of a grey water reuse system is compulsory, unless practically infeasible. Financial incentives are usually in the form of rebates for installing such a system. Municipal governments can also lead by example and procure such greywater reuse systems in municipal or city-run buildings, such as municipal offices or schools. This can not only improve the water-efficiency of such buildings, but can also showcase the benefits of the systems, and support local market demand.