Frequently asked water quality questions
This page offers answers to the most frequently asked questions about the water we supply.
Why does my water smell/taste of chlorine?
Chlorine is a powerful disinfectant which is used to make water safe to drink.
Chlorine has the advantage over other disinfectants of being effective from the treatment works right up to your tap.
You may occasionally detect a chlorinous smell/taste to your water following an operational change to our water treatment processes.
Why does water need to be disinfected?
Water is disinfected to make it safe to drink.
Disinfection plays an important role in protecting public health by killing harmful bacteria.
Why does my water appear white?
This is likely to be caused by trapped air in the pipework.
Air can be introduced into the water supply following repair work on the distribution network, or by a pocket of air becoming trapped in the internal domestic pipework.
What is hard water?
Hardness is caused by compounds of calcium and magnesium which occur naturally in water.
Those waters with a high concentration of calcium and magnesium are considered to be hard, while those waters with a low content are considered soft.
All supplies in our area are considered to be hard, although supplies in the Guildford region are slightly softer.
How do I find out the hardness of my water?
You can find out the water hardness level for your area by submitting your post code online.
Is fluoride added to my water?
We do not add fluoride to our water.
The decision on whether to fluoridate water supplies is taken by your local strategic health authority.
For more information on fluoride please contact your local health authority.
Why is my water brown and/or contain brown particles?
Brown discolouration or particles found in drinking water are commonly caused by iron.
Iron deposits can form from the corrosion of cast iron pipes and can become disturbed by flow changes in the network.
Although not harmful to health, care should be taken to avoid the use of water until it has cleared.
Is there likely to be lead in my water?
Lead is commonly found in the environment and can derive from sources such as vehicle exhaust fumes and old paint.
There is essentially no lead present in our drinking water when it leaves our treatment works.
The distribution network of mains, which transports drinking water to your tap, are not constructed from lead.
However, lead pipes have been used up to the 1970s to connect individual properties to the water mains.
In addition, if your house was built before the 1970s its internal plumbing may contain lead pipes.
Lead can leach from these pipes, or from lead solders used in copper piping, into the water supply.
What should I do if I lose water supplies or suffer from poor pressure?
If you are experiencing loss of supply or reduced pressure:
Please call our 24-hour Customer Centre on 0845 9200 800 (Minicom or Typetalk: 0845 7200 898).
If you are trying to contact us from outside the UK, please call +44 1793 366011.
They will be able to tell you if there are any issues or maintenance work taking place in your area.
Do pesticides get into drinking water?
UK and European regulations require water companies to test drinking water for the presence of pesticides to ensure levels are not exceeding the drinking water standard, which is almost zero - 0.1 micro grammes per litre, which is one part per 10 billion, or one drop in an Olympic-sized swimming pool.
Most of our 25,000 annual tests show that no pesticides have made it into our treated water supplies. However, samples do occasionally show detectable traces of, for example, weed killers like isoproturon, diuron and mecoprop, but these are almost always well below the stringent European pesticide standard.
In fact, the concentrations detected are so minute that they pose absolutely no risk to public health. If they did, the DWI (Drinking Water Inspectorate) wouldn't let us supply our water.
Following advances in detection methods, we've recently started to look for metaldehyde, the pesticide in slug pellets. Traces have been detected in treated water supplies by water firms across the country at levels fractionally above the pesticide standard.
It's impossible to completely remove metaldehyde from water using normal treatment methods. That's why we're working with manufacturers and farmers, the main users of slug pellets, to prevent metaldehyde from reaching water sources in the first place.
Experts say an average-size person would have to drink more than 1,000 litres - more than a tonne - of the worst-affected water (which is not in Thames water's supply area) every day of their lives to exceed the Health Protection Agency (HPA)'s 'acceptable daily intake' for metaldehyde.
