Where water comes from
Groundwater sources in Wiltshire and Dorset provide most of our supply.
Natural underground reservoirs, known as aquifers, are formed when rainwater sinks through rocks, such as chalk, limestone and sandstone.
To abstract this water, we sink boreholes as far as 120 metres into the rocks. Water can then be pumped to the surface, treated and distributed to customers.
Borehole water is usually free of the impurities found in other water sources so it needs less treatment.
It is injected with a solution of chlorine gas to kill off any bacteria and is sometimes aerated to replace carbon dioxide with oxygen.
The remaining water comes from 12 surface water reservoirs, fed by streams and rivers.
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