The water cycle
Our work at Severn Trent Water is an important part of the natural water cycle.
The amount of water on Earth is constant. The salt waters of the oceans and seas account for 97% of the world's water. Another 2% is frozen in the polar ice caps, leaving only the remaining 1% as fresh water for us to use.
The world has always had the same amount of water. Every drop we drink has been in a continuous 'water cycle' for billions of years. This means that every glass of water contains some water that may have been drunk before - possibly by dinosaurs or pharaohs (or your next door neighbour!) The water cycle simply recycles water over and over again.
We tap into this natural cycle, storing water in reservoirs, cleaning it before and after use and then returning it to the rivers and seas.
Naturally occurring fresh water is stored in natural lakes, as groundwater and as ice or snow on mountains. Groundwater is fresh water stored naturally beneath the ground in naturally occurring aquifers, artesian wells and as soil moisture or permafrost.
Heat energy (from the sun) causes water to evaporate (forming water vapour) into the atmosphere from sea, lakes and the soil. Ice and snow sublimate into water vapour. Plants transpire water from leaves and roots into the atmosphere.
Evapotranspiration is when evaporation e.g. from soil and plant transpiration combines with transpiration from plants.
Air currents containing water vapour rise over higher ground, taking vapour into cooler regions of the atmosphere. The cooler temperature causes condensation of water vapour to form clouds.
Air currents cause clouds to move around the Earth, across sea and land. As the clouds cool, precipitation occurs as snow, sleet, hail or rain. Most precipitation returns water to Earth into the oceans, seas, lakes and rivers. Some precipitation (over the land) runs off into streams and rivers or soaks down (infiltration) as soil moisture and may replenish groundwater reserves.
Humans abstract water from streams, rivers, lakes and groundwater sources including boreholes and wells. Abstracted water is stored in small quantities for personal use or in reservoirs ready for distribution and treatment by water companies.
Abstracted water is treated by Severn Trent Water at water treatment works. Treated clean water is distributed via pipes to homes, businesses and industry for use by customers: tested by EA and Drinking Water Inspectorate for quality.
Waste water from homes, businesses and industry is disposed of through Severn Trent Water sewers and drains. Waste water is cleaned at Severn Trent Water sewage treatment works.
Clean effluent from sewage treatment works is returned to streams and rivers: tested by EA for quality. Some groundwater reaches the surface of the land through springs and streams. Snow meltwater runs off into streams. Springs and streams run into natural freshwater lakes and rivers, eventually returning as saltwater to the sea or oceans.
