Rainwater and grey-water can be used instead of fresh-water in a number of applications, including toilet flushing, cleaning and irrigation, which reduces fresh- and waste-water volumes and corresponding costs. 

Grey-water is slightly polluted waste-water e.g. from showers or production. It can be easily treated and reused in different processes. Rainwater can be used in, for example, fire-fighting reservoirs, as cooling water or in heating systems. Rainwater can be collected from roof-tops, filtered and stored in reservoirs. Rainwater also contains no chalk, so less detergent or chemicals are needed when used for cleaning.

Using rainwater and grey-water can reduce the cost of fresh-water as well as for sewage. In addition to water-efficiency measures, water recycling can reduce fresh-water consumption by about 10 %, which has financial and environmental benefits, especially in water-poor regions trying to mitigate the impacts of climate change. 

The installation of rainwater and grey-water recycling systems is applicable to all new buildings. Retrofitting such systems to existing buildings is expensive and impractical unless the building is undergoing extensive renovation. Building ownership is also an issue for the renovation of buildings with these systems.