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How much chlorine is in my water?

We add small amounts of chlorine to drinking water supplies to ensure that it's safe for you to drink.

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Why we add chlorine to drinking water supplies

Even after water has been filtered we need to make it bacteriologically safe to meet the Water Supply (Water Quality) Regulations. This means we must disinfect your drinking water before distributing 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.

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.

Learn more about our water treatment process.

Frequently asked questions about chlorine

Here you can find answers to some commonly asked questions about chlorine residuals in water supplies.

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 the water after treatment. This ‘residual’ amount of chlorine ensures that the water stays bacteriologically safe as it passes through the distribution mains. 

In very long distribution networks, we sometimes add chlorine at strategic points. This helps us ensure there is enough throughout the whole length of the system. We call this 'boosting'. These residual amounts of chlorine are also monitored at the water supply works, service reservoirs and customer taps using field monitoring kits.

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 also extremely sensitive to chlorine.

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.

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