How we test your water

We continuously monitor water quality to ensure customers receive a safe supply of drinking water.


We analyse 50,000 samples of water from treatment works, reservoirs and customers’ taps annually. In the unlikely event of a problem arising at a site, it is shut down automatically.

Analysis is carried out using sophisticated laboratory instruments, and many results are close to the lowest detectable levels.

This analysis covers three areas:

  • physical, which examines the basic character and behaviour of water
  • chemical, which measures the level of specific substances
  • microbiological, which ensures that no harmful microorganisms are present.

What we test for

Below is an A to Z list of the substances we test for and the levels of them that can be present for water to be considered safe.

We measure these substances using:

  • mg/l = milligrams per litre or parts per million
  • µg/l = micrograms per litre or parts per billion
  • Bq/l = becquerel per litre unit of radioactivity (equal to one disintegration or nuclear transformation per second).

What to expect if we need to test your water

We carry out water sampling visits at randomly selected properties to test our supply – find out what to expect if your home is selected.