The water cycle
Water is constantly recycled naturally as part of the water cycle. Water returns to Earth from the sky as precipitation (rain, hail or snow). Some water flows along or through the ground, evaporating back into the air from waterways - or taken up by plants and released by transpiration. The water then rises invisibly into the air, condensing to form clouds and continuing the cycle.
Our drinking water comes from the part of the cycle between precipitation and evaporation. Next time it rains, watch the water flow downhill and collect in puddles. This is a tiny model of a catchment. The runoff from a catchment is collected in reservoirs, filtered and then piped to your home. The water sits in reservoirs for some time before being piped to the filtration system. This allows the sediments to settle out of the water, just as powdered chocolate settles in a glass of milk if you leave it for too long.
Wastewater and sewage consists of water going down the drain from your toilet, laundry, sink, bath and shower -- plus waste from factories and other industries. Wastewater is 99 per cent water, but it must be treated before it is either released into the environment or used again. Most sewage is released into the sea after treatment, but some inland waste is treated and returned to the catchment.
