How much chlorine is in my water?

Find out how we use chlorine to make water safe to drink.

Even after water has been filtered it needs to be made bacteriologically safe to meet the Water Supply (Water Quality) Regulations. This means your drinking water must be disinfected before we distribute it through our supply pipes. We do this to ensure that any harmful bacteria are killed. One method of doing this is to use chlorine.


A safe way to disinfect water

Chlorine has been used for over 100 years to disinfect water. It’s harmless to people at the small concentrations we use in our supplies. Effective disinfection is vital to prevent waterborne diseases.


How we add chlorine to disinfect the water

The way we disinfect drinking water is to add tightly controlled amounts of chlorine at our water supply works. A small amount of chlorine remains in water after treatment. This ‘residual’ amount of chlorine ensures that the water stays bacteriologically safe as it passes through long lengths of distribution mains. In very long distribution networks, we sometimes add chlorine at strategic

points (boosting) to make sure there is enough throughout the whole length of the system. These residual amounts of chlorine are also monitored at the water supply works, service reservoirs and customer taps using field monitoring kits.


If your water tastes or smells of chlorine

You may not notice, but every water supply has its own distinct taste due to its chemical composition.

This is why you may notice a difference when you travel to a different area of the country. Taste problems in water are partly due to salts and the presence of specific metals such as iron, copper, manganese and zinc. The difference can be more noticeable due to the degree of softness or hardness of your water. Some people are also more sensitive to tastes and odours than others, which mean that some may notice a slight taste which others may not. Some customers are more sensitive to the taste of chlorine than others.

You may also be more aware of the taste and smell if:

  • a water main near you has been replaced. This is because the new main doesn’t ‘absorb’ chlorine in the way the old mains did
  • you live close to the water supply work
  • you live close to a service reservoir/tank where secondary chlorination (boosting) is used to increase the residual amounts needed to keep the water safe.


What you can do about it

If you can smell or taste chlorine in the water from your tap, the following process should help:

  • Run some water from your kitchen tap into a clean jug.
  • Cover the jug with a clean cloth and let it stand in the fridge until chilled. Cold water doesn’t just taste better, but letting the water stand helps the residual chlorine level to reduce.
  • Don’t drink the water in the jug after 24 hours because bacteria may start growing again making it unsafe to drink.

Water may sometimes taste or smell different to normal and this can be for a number of reasons.


If you have pet fish

Residual levels of chlorine are harmless to domestic pets but can affect fish and amphibians such as frogs and turtles. Fish kept in aquariums or ponds are extremely sensitive to chlorine.

So when you’re filling or topping up aquariums, you should try to remove the chlorine before water comes into contact with the fish – aquatic and pet shops can offer suitable products and advice to do this.