Sutton and East Surrey Water

Where our water comes from
The geology of the region means much of our water (85%) comes from underground.

When it rains, water runs into streams and rivers and soaks into the ground. In spring and summer, much of it evaporates or is used by plants and trees. In winter, the rain seeps into the topsoil and into the rock beneath the surface. This water holding rock, or aquifer, acts like a giant sponge.

The rock is either chalk or greensand and boreholes are sunk at a depth of between 90m - 180m. The water is pumped to the surface, and then piped to our treatment works.

The rest of our water (15%) comes from our reservoir at Bough Beech, which is filled from the River Eden in Kent, during the winter.

How our water is treated
Water from boreholes is of high quality, because the chalk and greensand acts as a natural filter. However, it still needs to be purified before it is safe to drink. We further improve the quality of the water by a treatment process called 'softening'.

The water extracted from our boreholes is known as 'temporary' hard water. That means that it contains dissolved minerals, i.e. calcium and magnesium bicarbonates, which when mixed with soap, produce a solid precipitate called 'scum'. Also, if this water is heated, a solid precipitate called 'scale' is produced.

Softening makes the water much more pleasant to use and reduces the amount of soap and other detergents needed. It also reduces scaling in tanks, boilers and kettles. Softening therefore keeps household costs down and helps the environment.

River water needs a different type of treatment process. In general, it needs more filtration and treatment to remove taste and smell.

This diagram illustrates each stage in the treatment process employed by Sutton and East Surrey Water to treat river and borehole water.

RIVER	AQUIFER
SCREENING Leaves and large debris removed	AERATION Water from aquifers contains dissolved carbon dioxide (CO2) and to remove it we blow air through the water. If we leave the CO2 in the water we will use more lime at the later softening stage. Aeration also converts soluble salts of iron and manganese, that occur naturally in the water, into insoluble precipitates which are subsequently removed.
CHLORINATION Chlorine is added to purify the water	CHLORINATION Chlorine is added to purify the water
CLARIFICATION Fine particles are removed by adding coagulants, that cause the particles to stick together to form large lumps, called floc, which settle out of the water.	SOFTENING The water then moves to the softening tank. Lime, fine sand or a coagulant are added. The lime reacts with the bicarbonates, which cause the hardness, to form chalk. The chalk is either deposited on the fine grains of sand to form pellets, or the particles of chalk coagulate into a sludge, both will settle on the bottom of the tank. The softened water leaves the top of the softening tank to the next stage.
FILTRATION The water passes through gravity filters containing sand which remove any fine particles which have not settled. Carbon Pressure filters containing 'Granular Activated Carbon' remove taste, smell and very fine particle	FILTRATION The water passes through gravity filters containing sand which remove any fine particles which have not settled. Carbon Pressure filters containing 'Granular Activated Carbon' remove taste, smell and very fine particle