Water Supply Works

Water supply works treat water from rivers using many different processes. The treatment cleans water so that it is safe for people to use in their homes. Scientists check that the water meets the required standards before it is pumped through pipes into people's homes.

At some works, such as Burham near Maidstone, water is taken from the river and pumped into a lake. This is because the water can vary in quality. The water stays in the lake for about one week. Small particles of clay, plant matter and sand settle to the bottom of the lake. The water then leaves the lake at the other end by a draw-off tower. The water is then pumped to a water supply works.

Inlet retention chambers

The water then enters a tank. From there it goes into inlet retention chambers. A chemical called aluminum sulphate is added to the water. The chemical reacts with the water to produce a fluffy white mass called floc. In the second inlet retention chamber, a chemical called polyelectrolyte is added. This turns the floc into a solid blanket.

The floc in the inlet retention chamber	An inlet retention chamber where the floc is a solid

Clarification process

The water and the chemicals then go into clarification tanks. The water enters the bottom of the tanks. The floc forms a layer on the top of the water. Because the floc is heavier, the water rises up and passes through this blanket. The floc traps large particles of impurity in the water.

The cleaned water then flows into collecting troughs at the top of the clarification tanks. The troughs then take the water to the filters. There are cones in the clarification tanks which collect the floc. The extra floc is pumped away to a lagoon.

Clarification tanks

After this stage, water is collected in the troughs in the middle.	The red cone collects the excess floc.

Filtration

The next stage of treatment is primary filtration. There are normally eight filters. The water travels downwards through the filters. Small particles of impurity are removed. The filters gradually get smaller from the start to finish of this stage of the process. This is so that the small particles of impurity can be trapped in the filters.

The water at Burham then passes into the Works Intermediate Pumping Station. Here, the water is pumped into ozone contact tanks. Ozone gas is pumped into the water to break down any pesticides in the water. The ozone is pumped via generators from oxygen tanks.

The building with the Ozone contact tanks and Adsorbers	The ozone generators

The water then leaves the ozone contact tanks. Sodium biosulphate is added to remove any of the ozone still in the water. The water then goes into Adsorbers. Inside the Adsorbers is a substance called granular activated carbon. The carbon acts rather like a magnet. Any pesticides in the water are attracted to the carbon. They stick on to it like iron filings to a magnet.

The adsorbers

Sterilisation

Sterilization is the final stage of the process. The water goes into a large tank called a contact tank. Sodium hydroxide and chlorine are added to the water. This is to kill all the remaining bacteria and to make sure that the water has the right pH (not too acidic or alkaline).

The water then flows into a clear water tank. The water can then be pumped by pipes to service reservoirs. Service reservoirs are huge underground tanks where clean water is stored. Water leaves the reservoir by pipes, to go on its way to our homes.

The clear water tank