Sutton and East Surrey Water

Aerator - A device for blowing air through water.

Ammonia - Chemical added to make sure chlorine remains active while the water is in the distribution system.

Aquifer - An underground layer of porous rock, eg chalk and greensand, that can hold a large amount of water or allow water to flow through.

Borehole - A hole drilled into an aquifer in order to extract groundwater.

Chalk - Soft, white, sedimentary rock of calcium carbonate. Acts as an aquifer.

Chlorine - A gas (Cl2) added to water in small quantities to disinfect it by killing harmful bacteria.

Clarification tank - A tank where particles can settle out of water to make it clearer.

Clay - A rock made up of tiny particles that is impermeable to water. Underlies much of the Weald of Kent, including Bough Beech Reservoir.

Coagulation - The sticking together of tiny particles suspended in the water to form bigger particles ('floc') which sink more easily.

Coagulant - A chemical that helps particles clump together.

Condensation - The change of a vapour or gas to a liquid when cooled. For example, water vapour turns back to water droplets which form clouds in lower temperature areas of the sky.

Contact tank - Tank in which water is held during chlorination.

Evaporation - The change of a liquid to a vapour when heated. For example, water turns to water vapour when heated by the sun.

Filters - Normally a sand or carbon filter which trap particles carried in the water.

Greensand - A series of sandstone rocks forming a narrow ridge to the south of the Downs. Acts as an aquifer.

Groundwater - Water below the ground. Our water is often very pure as it is naturally filtered by the chalk and greensand aquifers through which it flows.

Hard water - Water that contains dissolved minerals, i.e. calcium and magnesium bicarbonates.

Precipitation - The formation of rain, hail or snow.

Raw Water - Untreated water from borehole or reservoir.

Sludge - Solid waste material removed during water treatment.

Sulphur dioxide - SO2 added to water to remove excess chlorine and thus control concentration at the optimum level for disinfection in the journey to customer's taps.

Surface water - Water above the ground i.e. rivers, lakes and reservoirs.

Water cycle - How water circulates in the environment.

Water table - The level of water in the aquifer.