Water treatment

Water treatment

Depending on where you live, it is likely that your water supply originates from deep underground in Wiltshire and Dorset - 80% of our water comes from there and the remainder from reservoirs.

The water in natural underground reservoirs - aquifers - fell to the ground before seeping through rocks such as chalk, limestone and sandstone.

Boreholes sunk up to 120 metres into the rocks enable us to pump this water to the surface before treating and supplying your home.

Water sourced from aquifers is usually free of impurities and needs less treatment.

We simply inject it with a solution of chlorine gas to kill off any bacteria and in some cases aerate it to replace carbon dioxide with oxygen.

If your water is not supplied from groundwater sources, it will come from our 12 surface water reservoirs which are fed by streams and rivers.

Reservoir water needs a higher level of treatment than groundwater. We use a number of different processes to purify water to the high quality required by law.  

The most common methods are sand filtration and dissolved air flotation where the water arriving at a treatment works flows through fine filters to remove algae, insects and any other objects.

Dissolved air flotation: Water is fed into a chamber where chemicals are added to make any particles stick together. Air is pushed up through the water forcing the particles to the surface where they are then removed.

Sand filtration: The water flows into fine sand filter beds which trap any remaining particles. The water is cleaned further by passing it through filters which trap any remaining particles.

In both methods filtered water is treated with lime to reduce acidity and chlorine to kill any germs.

Coagulation: A small amount of chemical coagulant is added to help bind together any impurities so that they stick to the sand filters, which are cleaned regularly.