What Is the Level of Chlorine in UK Tap Water?

Sep 10, 2025

5 min read

Updated: May 5

What is Chlorine?

Chlorine is a chemical disinfectant widely used to prevent the spread of waterborne diseases. It is one of the most common treatment chemicals in drinking water worldwide.

What levels are found in UK water?

Chlorination was first introduced into UK drinking water in 1905 in Lincoln, after a deadly typhoid outbreak killed more than 100 people. The emergency use of chlorine eliminated the outbreak, and by the 1920s, routine chlorination became standard across the UK.

Today, UK water companies maintain chlorine at around 0.5–1.0 mg/L at treatment plants, gradually reducing to 0.1–0.8 mg/L by the time water reaches consumers’ taps. This “residual chlorine” ensures protection against bacterial regrowth in the distribution system.

Levels are carefully regulated and kept well below the WHO safe guideline of 5 mg/L. Still, variations can occur depending on local infrastructure, distance from treatment works, and seasonal adjustments (e.g., higher chlorine levels in summer when bacteria multiply faster).

In the DWI's words: “Typically, water companies keep the level of residual disinfectant in the form of free or combined chlorine to 0.5 mg/l or less.” “However sometimes during maintenance of the pipe network, higher levels are needed.” And on the WHO figure: “The World Health Organisation has set a health-based guideline maximum value of 5 mg/l for chlorine as a residual disinfectant in drinking water.” “The levels in tap water in England and Wales are well below this guideline”. (DWI)

Why does my tap water smell of chlorine some days more than others?

Three things change the level at your tap:

Distance from the treatment works. The DWI says “if your property is located near to the water treatment works the level of chlorine may be a little higher in your tap water than it is at properties several miles further away.” (DWI)
Work on the network. “If you occasionally notice a slight taste or smell of chlorine, it is probably due to maintenance work in your area, it will not be a long lasting problem and there is no cause to worry.” (DWI)
How long the water has stood in your pipes. Chlorine fades over time, so water that has sat for a while can smell different.

When to report it: “If you notice a particularly bad or strong smell or TCP like taste which makes your tap water unpalatable, or you notice a smell or taste for the first time which does not go away in a short time, then you should contact your water company immediately.” (DWI)

A “TCP” or antiseptic taste is different. “Chemical reactions can occur between chlorine and chemicals in kettles, rubber or plastic components within your domestic plumbing system, which lead to antiseptic and medicinal tastes.” (DWI) “A common cause of TCP like tastes is the hoses that are used to connect domestic appliances to the water supply.” (DWI)

More on odd tastes and smells: Cloudy, Brown or Funny-Tasting Tap Water? A Symptom-by-Symptom UK Guide.

What are the health effects of Chlorine?

The DWI says: “At the very low levels used in drinking water, it is a proven public health measure for safety and effectiveness and is perfectly safe to drink.” (DWI) What people do notice:

Taste and smell: “The reason why chlorine can be a concern in drinking water relates to the fact that some people can be very sensitive to its taste and smell.” (DWI)
Disinfection by-products (DBPs): When chlorine reacts with organic matter, it forms by-products like trihalomethanes (THMs). These are regulated: the EU sets THM limits at 100 µg/L, and the UK standard for total trihalomethanes is also 100 µg/L.

Free chlorine vs total chlorine: what a test reading means

Reading	What it measures
Free chlorine	Chlorine still available to disinfect. It's usually the part you smell.
Total chlorine	Free chlorine plus combined chlorine, such as chloramine (chlorine combined with ammonia).

The DWI refers to residual disinfectant “in the form of free or combined chlorine” (DWI). If a kit shows both readings and total is noticeably higher than free, some of the chlorine in your supply is in combined form. Your water company can tell you which it uses.

Reading tips: read at exactly the time the kit instructions give, in daylight, against a white background. Colours can keep developing, so reading late can overstate the result. Our chlorine test reads 0 to 1 ppm, with a minimum detection of 0.05 ppm.

What can be done?

If taste or smell bothers you, letting tap water stand uncovered or chilling it in the fridge can help chlorine dissipate. But the only way to know the actual chlorine level in your home is through testing.

The DWI's simple fix: “If you do not like the smell or taste, then a simple way to remedy the problem is to place a jug of tap water in your fridge for a short period, this will reduce the chlorine smell and/or taste.” “Always remember to throw away any unused water after 24 hours and clean the jug regularly.” (DWI)

Activated carbon filters are widely used to reduce chlorine taste and smell. The DWI says “if you wish, you could always try using a simple jug filter with an activated carbon cartridge.” (DWI) If you buy one, check what it's independently certified to reduce, and change the cartridge on time.

FAQs

How much chlorine is in UK tap water?

“Typically, water companies keep the level of residual disinfectant in the form of free or combined chlorine to 0.5 mg/l or less.” “most water companies aim to keep the level below 1 mg/l.” (DWI)

Is it safe to drink tap water that smells of chlorine?

The DWI explains why it's there: “Water is safe when it leaves the water treatment works and the trace of chlorine is there only to preserve the high quality of the water as it passes through the miles of pipes used to convey water to homes and workplaces.” (DWI)

How long should tap water sit to remove chlorine?

There's no official time. The DWI's advice is simpler: “Cooling tap water in the fridge is all that is needed.” (DWI) Throw away anything unused after 24 hours.

What does “free chlorine” mean on a test?

It's the chlorine still available to disinfect, usually the part you smell. “Total” adds combined forms such as chloramine.

How can I find out my area's chlorine level?

“Your water company will provide you with a free water quality report showing the maximum and minimum level of residual chlorine in your local water supply on request.” (DWI) Already tested? Check what your chlorine reading means.

Conclusion: Chlorine protects public health, and the DWI says levels are typically 0.5 mg/l or less. A home test tells you whether your own tap is typical, or worth raising with your water company.