Greywater is water that has been used already in the home, such as in the shower, bath, hand-basin or washing machine. Greywater recycling methods range from simple diversion units used for the garden to sophisticated systems that treat the water for reuse in the toilet and laundry.

Untreated greywater may contain pathogens, contaminants such as salts and other substances harmful to human health and the environment. It is therefore recommended that only laundry rinse water and shower water is reused in greywater systems.

WestWyck, however, is developing a recycling process that includes all used water, including toilet waste (black water). The liquid waste is pumped through a series of evapo-transpiration beds, where it is absorbed and processed by specially chosen plants such as woolly ti-trees and reed beds.