Types of Water

The process of collecting, treating, and reusing water such as rainwater, surface water or grey water at or near its source is called decentralised water reuse. Types of water sources for which well-tested and scalable technologies exist today and that are most often reused include rainwater, stormwater and greywater.

These types of water are defined as follows:

Rainwater is precipitation from a rain or snowmelt event that is collected directly from a roof surface not subject to frequent public access. It is considered the cleanest water after mains water as under normal conditions it has limited sources of contamination, primarily small amounts of faecal matter from birds and animals and roof and drainage materials. In fact, in some areas of the world rainwater is considered of sufficient quality to be used for drinking. 

Stormwater is defined as precipitation runoff from rain or snowmelt events that flows over land and/or impervious surfaces (e.g. streets, parking lots, and roofs, including roofs with frequent public access). Compared to rainwater, stormwater has additional sources of contamination, including hydrocarbons, PFAS, nutrients, heavy metals, microbial content, suspended solids and other types caused by vehicles, birds, animals, soil, air, surfaces and human waste. 

In England, British Standard BS EN 16941-1 provides guidance on design, installation, maintenance and risk management of rainwater and stormwater harvesting systems. 

Greywater is defined as wastewater collected from sources such as bathroom sinks, showers, bathtubs and clothes washing. Greywater can be contaminated by chemicals and metals from personal care and cleaning products, microbial content, raised temperature and microplastics. 

In England, British Standard BS EN 16941-2 provides guidance on design, installation, maintenance and risk management of greywater recycling systems.