Although not common in the UK at present, many other countries have pioneered the use of Treated Wastewater (TWW) for use in non-potable situations. This water can be defined as water that has been used in a domestic, commercial, agricultural or industrial setting. The majority of domestic wastewater is sewage, drainage or grey water, whilst commercial, agricultural and industrial water can be drainage, by-product water or sewage.
The majority of this water comes from the sewage network and sewage treatment plants. Currently in the UK, most of the water from sewage treatment plants is discharged to river networks after a series of treatment stages. This is estimated to be around 4 billion m3 a year. Most of this water is discharged in a good condition which would allow it to be used as irrigation water, subject to additional on-site treatment, i.e., UV disinfection.