How we treat your water
A lot goes on at our water treatment works to make your water safe for drinking.
The extent of the treatment varies depending on where we collect the water from - if it's from a borehole the water usually only requires minimal treatment, if it's from lowland river sources and upland reservoirs it will go through a tougher treatment process.
When water reaches our works it will normally go through the following stages:
Screening
The water passes through a huge metal strainer to remove things like leaves and twigs.
Flocculation
Approved chemicals are added to act like a magnet for smaller impurities like dirt, natural colour and bacteria. The chemicals form a sort of jelly called floc.
Clarification
The floc has to be taken out of the water, so air is bubbled through the tanks to make the floc float to the surface to form a blanket, where it is scraped off. This process is called Dissolved Air Flotation or DAF for short. At some works that don't have DAF, the floc instead sinks to the bottom of the tanks and is taken away - this process is called sedimentation
Filtration
The clarified water is passed through filters filled with layers of sand and gravel to remove any final traces of the floc and metals such as iron and manganese. These filters are cleaned regularly, every one or two days.
Ozonation
Ozone is a gas which is a powerful oxidant and is used at a few of our water treatment works. It's bubbled through the water to remove any traces of pesticides or similar compounds.
Granular Activated Carbon
Granular Activate Carbon is used in filter beds to remove the by-products of ozonation, as well as traces of any other substances which may also be found in the water.
Chlorination
Chlorine is then added to the water. This kills off any microbes that may still be present. A small amount of chlorine is left in the water as it travels to your home to ensure the water at your tap is of the highest possible quality.
