If the water that came out of our taps looked like the water we get from a river then we wouldn’t want to drink it. It is dirty and has lots of things living or floating in it.
We clean the water to take the colour and the dirt out of it and to remove any germs. The germs that can be found in unclean water could cause diseases like typhoid, cholera and diarrhoea. It is these diseases that cause nearly 6000 children to die everyday in the developing world. Even at the beginning of the 20th century these diseases were killing people in this country.
There are four main stages in water treatment:
Taking water out of a river or other water source
• Water from a river, reservoir or borehole is pumped into the water treatment works
• It goes through screens made from metal with holes in that allows the water through but not leaves, branches or any other debris. The water then passes into large storage tanks.
Making the water clearer by removing the dirt and colour
• The water contains dirt, colour, bacteria and viruses that need to be removed
• In the flash mixer we add a chemical called ferric sulphate to the water. This acts as a magnet and attracts the dirt to collect together and become a floc
• A polymer is added to help the floc stick together
• Carbon may also be added to remove pesticides and lime to alter the acidity or alkalinity (pH) of the water
• The water flows into the clarification tanks
• The floc (dirt particles) start to get bigger and heavier and sink to the bottom forming a blanket of sludge
• The sludge is drawn off, dried and recovered to agricultural land as a soil conditioner
• The cleaner, settled water flows from the tank over the edge (launder) into a channel and on to the filters
Filtering the water to trap anything floating in it
• The water goes through to large tanks filled with layers of charcoal, gravel and sand
• The water passes through these layers and any left over bits of dirt or particles of chemical are trapped leaving the water clean
Disinfection killing any germs
Although the water looks very clean it still contains germs, which are the most important things we need to get rid of as they can make us very poorly. We use a chemical called chlorine to kill the germs.
At all points along the way the water is continuously tested and monitored to ensure the right amount of chemicals are being added and that the water is flowing smoothly. Now the water is clean and safe to drink it can be sent down the water pipes to our homes, schools, businesses, leisure centres, etc.
Download the PDF version of the water treatment process.