All UK water companies add chlorine to drinking water by law. The taste is normal — but levels vary by zone. Enter your postcode to see your area's measured chlorine level.
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Without chlorination, waterborne disease epidemics would return. The taste is harmless at UK levels. If you dislike it, a standard filter jug removes it completely.
Chlorination of public water supplies is one of the greatest public health achievements of the 20th century. Before widespread chlorination was introduced in the UK in the early 1900s, waterborne diseases — typhoid, cholera, dysentery — killed tens of thousands of people each year. Chlorine kills pathogens rapidly and cheaply, and unlike boiling, it maintains a residual concentration throughout the distribution network.
UK water companies are legally required under the Water Supply (Water Quality) Regulations 2016 to ensure treated water contains sufficient disinfectant residual to prevent microbial contamination at the customer's tap. The minimum detectable residual at the tap is typically set at around 0.1 mg/L by most companies, with the DWI guideline maximum of 0.5 mg/L.
No. At concentrations found in UK tap water — typically 0.1 to 0.3 mg/L — chlorine is not harmful to drink. The WHO's health-based guideline value is 5 mg/L, which is ten times higher than the UK maximum guideline. You would need to drink water at WHO guideline levels for many years before any health effect would be plausible.
The more nuanced concern relates to disinfection byproducts. When chlorine reacts with naturally occurring organic matter in source water — humic acids from soil and vegetation — it forms chlorinated compounds including trihalomethanes (THMs) such as chloroform, bromodichloromethane, and dibromochloromethane. These are regulated at 100 µg/L in the UK (a group total, called TTHMs). Long-term exposure to THMs above these levels has been weakly associated with bladder cancer in epidemiological studies. However, UK tap water almost universally complies with the 100 µg/L limit.
Chlorine is detectable by smell at around 0.2 mg/L and by taste at 0.3–0.5 mg/L for sensitive individuals. The taste varies: chlorine reacting with organic matter produces chloramines and chlorophenols, which can smell medicinal or swimming-pool-like. Some people are highly sensitive; others don't notice it at all.
Water companies are required to test for taste and odour. If your water has a strong, persistent chlorine taste significantly beyond what you normally notice, it's worth reporting to your water company — it may indicate an issue at a booster chlorination point or a change in supply source.
An increasing number of UK water companies use chloramine (a compound of chlorine and ammonia) as a secondary disinfectant, either instead of or in addition to chlorine. Chloramine is more stable than free chlorine and provides a longer-lasting residual in distribution networks, which is why it is favoured for large, complex systems.
The important practical difference: chloramine does not off-gas on standing, unlike free chlorine. If your water company uses chloramine and you want to remove it, you need a catalytic activated carbon filter rather than a standard granular activated carbon filter. Check your water company's annual report to find out which disinfectant they use.
Research on chlorinated water and gut microbiome is at an early stage. Some animal studies and in vitro experiments suggest that chlorine at concentrations of 0.5–1 mg/L can alter microbial communities. A few human observational studies have found correlations between chlorinated water and reduced microbiome diversity. However, these studies have significant confounders and have not established causality at normal UK tap water levels (0.1–0.3 mg/L).
If you are particularly concerned about gut microbiome health — especially relevant for those on antibiotics, recovering from gut dysbiosis, or with IBD — using a carbon-filtered water source is a low-cost precautionary measure. It costs nothing to add a filter jug to your routine and removes the question entirely.
An activated carbon filter is the simplest and most cost-effective solution. All standard filter jugs — Brita, BWT, Waterdrop, and others — use activated carbon that adsorbs chlorine and chloramines (with catalytic carbon) with near-complete efficiency. Additional options:
Chlorine is added to tap water as a disinfectant — it kills bacteria, viruses and other pathogens in the water and, critically, maintains a residual concentration throughout the distribution network to prevent microbial regrowth. UK water companies are legally required under the Water Supply (Water Quality) Regulations 2016 to treat water to ensure it is safe from microbial contamination. Chlorination is the most widely used and cost-effective method. Without it, waterborne diseases such as typhoid, cholera, and cryptosporidiosis — which historically caused mass casualties — would return. The chlorine taste and smell, while unpleasant to some, is a sign the disinfection system is working.
Yes, at the levels found in UK tap water, chlorine is safe to drink. The UK maximum is 0.5 mg/L (the DWI guideline). Most tap water is tested at 0.1–0.3 mg/L. The WHO guideline value is 5 mg/L — ten times the typical UK level. At normal tap water concentrations, chlorine is not toxic and there is no evidence of direct acute health harm from drinking it. Long-term concerns relate to disinfection byproducts (DBPs) rather than chlorine itself: when chlorine reacts with organic matter in the water, it forms trihalomethanes (THMs) and haloacetic acids (HAAs). THMs are regulated at 100 µg/L in the UK and are weakly associated with bladder cancer risk at sustained high exposure.
A detectable chlorine taste or smell is completely normal and indicates the disinfection system is working. Chlorine becomes detectable by smell at around 0.2 mg/L and by taste at around 0.3–0.5 mg/L for sensitive individuals. If the taste is stronger than usual, it may indicate: (a) water that has travelled a long distance through the distribution network with diminishing residual — the company may add more chlorine at booster points; (b) water from a different source than usual (e.g. a seasonal switch to reservoir supply); (c) low consumption periods such as summer holidays, when water sits longer in mains. A persistent very strong chlorine taste is worth reporting to your water company.
This is an area of active research, and the honest answer is: possibly, at the higher end of normal tap water concentrations. In vitro and animal studies show that chlorine at concentrations of 0.5–1 mg/L can affect bacterial communities. A small number of human observational studies have found associations between chlorinated water consumption and reduced gut microbiome diversity, but causality has not been established. UK tap water at 0.1–0.3 mg/L is well below concentrations that cause demonstrable microbiome disruption in most studies. If you are concerned about gut health, an activated carbon filter will remove virtually all residual chlorine before it reaches your gut.
The simplest and cheapest method is an activated carbon filter jug — standard filter jugs including Brita, BWT and Waterdrop models all use granular or block activated carbon that adsorbs chlorine highly effectively. A good filter jug removes 98–99% of chlorine. Alternatively: (a) leaving water to stand in an open container for 30–60 minutes allows chlorine to off-gas naturally; (b) inline under-sink carbon filters remove chlorine for all kitchen water; (c) reverse osmosis systems also remove chlorine as the pre-filter stage. Note: chloramine (used by some water companies as an alternative to chlorine) does NOT off-gas on standing and requires a catalytic carbon filter rather than a standard carbon filter to remove effectively.
Chlorine levels are typically higher in zones that are furthest from treatment works — at the 'ends' of long distribution networks where the residual concentration must remain sufficient. Large urban areas with complex distribution systems, including parts of London (Thames Water), the North West (United Utilities), and Tyneside (Northumbrian Water), can see higher chlorine residuals than zones close to treatment works. Areas that periodically switch between surface water sources (typically higher organic content, requiring more chlorine) and groundwater sources (lower organic content) may also experience seasonal variation. Enter your postcode above to see your zone's measured chlorine mean.
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