To provide water that's good for you, we have to meet the drinking water quality standards set by the Water Supply (Water Quality) Regulations.
The type of treatment process required depends on the type of raw water source and its quality in a particular area.
Water from springs and boreholes is generally higher quality and may only need basic treatment followed by disinfection. Water from sources such as rivers, lakes and reservoirs, will normally require more complex treatment as it may contain more impurities (for example, pesticides) that have to be removed.
We monitor the quality of our raw water sources to make sure they haven’t become contaminated – and also to decide which type of treatment to use for a particular source of raw water. Follow the link to find out more about how we monitor, test and maintain water quality.
Treatment of water depends on the source, so any particular water supply works may use one (or more) of the processes below. We don't add fluoride to water – find out about the natural levels that occur.
Surface water is stored in reservoirs to provide an adequate supply to meet demand throughout the year. This also enables particles to settle. Ultraviolet light from the sun helps to reduce bacteria levels and break down organic compounds in the raw water.
Water is passed through mesh screens which remove larger-sized material in raw water such as leaves, weeds and sticks.
Particles are removed through the processes below:
Granular activated carbon (GAC) is used to remove many tastes and odours. The process causes the materials responsible for taste and odours to be absorbed by the particles of GAC. It's often used during the summer when taste and odour problems are more likely to occur, as well as being used to remove pesticides from drinking water supplies.
The scientific term pH is used to describe the degree of acidity or alkalinity. The pH levels of water need to be controlled because if water is too acidic it may corrode distribution and domestic pipes, while if it’s too alkaline, it may cause deposits to form inside the pipes or cause taste or odour problems.
Satisfactory disinfection is vital to prevent waterborne diseases and to ensure we supply water that meets the Water Supply (Water Quality) Regulations. Chlorine is used for disinfection either in gas or liquid form. Other disinfection processes include use ultraviolet light (UV) or ozone.
Lead can be present in domestic pipe work and the pipes connecting to the water mains. Phosphates may be added at water supply works to help prevent lead being leached into the water from the pipes.