PACIFIC Mains water supplied to households is used for many purposes, other than drinking and food preparation, notably bathing and showering, toilet flushing and the washing of utensils, dishes and clothes. Except where main drainage is not installed, the used water gravitates to the local sewer and becomes ‘sewage’. Domestic wastewater will contain both solid and dissolved pollutants including faucal matter, paper, urine, sanitary items, food residues and a variety of other contaminants. The sewer network will usually also receive wastewaters from office and commercial properties and from industrial premises. Rainwater from roofs and roads may also drain into the sewer network.