What’s in UK tap water? Chemicals, limits and local results

Fluoride

Fluoride occurs naturally in many water sources. In some areas it is also added through a fluoridation scheme; the Drinking Water Inspectorate (DWI) says schemes aim for 1 mg/l. The amount measured does not tell you whether it was added. Suppliers monitor it because the law sets a maximum.

Legal limit (England): 1.5 mg/l (as F). Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

Read our fluoride guide for natural fluoride, fluoridation schemes and how to read the units.

Published fluoride results on WaterGrade: Severn Trent Water, 1,357 pages (for example Aston New Town); Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Wessex Water, 404 pages (for example Cranmore); United Utilities, 62 pages (for example Lancaster); Yorkshire Water, 34 pages (for example Bradford).

Lead

Source water rarely contains lead. It gets into tap water mainly from lead pipes, lead solder or fittings, most often in homes built before about 1970. Suppliers test at customers’ taps and treat water to reduce how much lead dissolves from pipes.

Legal limit (England): 10 µg/l (micrograms per litre). Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

An area result cannot rule out lead from the pipes in your own home. Read our lead pipes guide to find out how to check your pipes.

Published lead results on WaterGrade: Severn Trent Water, 1,357 pages (for example Aston New Town); Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Wessex Water, 404 pages (for example Cranmore); United Utilities, 62 pages (for example Lancaster); Yorkshire Water, 34 pages (for example Bradford).

Nitrate

Nitrate reaches rivers and groundwater mainly from farm fertilisers and manure. Suppliers monitor it, and blend or treat water where levels in a source are high. Nitrite, a related compound, has its own limit.

Legal limit (England): 50 mg/l (as NO₃). Nitrite: 0.50 mg/l at consumers’ taps. Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

Regulation 4 also requires nitrate/50 + nitrite/3 to be no more than 1 (regulation 4). DWI says the 50 mg/l nitrate standard is based on the World Health Organization guideline value, which is also 50 mg/l.

Published nitrate results on WaterGrade: Severn Trent Water, 1,357 pages (for example Aston New Town); Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Wessex Water, 404 pages (for example Cranmore); United Utilities, 62 pages (for example Lancaster); Yorkshire Water, 34 pages (for example Bradford).

Chlorine and chloramine

Suppliers add a small amount of chlorine to disinfect water, and keep a low level (the “residual”) in the pipes to protect it on the way to your tap. Some supplies use chloramine, a combination of chlorine and ammonia that lasts longer in the network; Scottish Water, for example, says more than a quarter of its customers receive chloraminated water. DWI says companies typically keep the residual at 0.5 mg/l or less. Chlorine is the most common reason tap water tastes or smells like a swimming pool.

Legal limit: the Regulations set no numerical limit for chlorine residual. Suppliers monitor it to control disinfection and taste. A lower number is not automatically better. Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

Why tap water can taste of chlorine

Published chlorine residual results on WaterGrade: Severn Trent Water, 1,357 pages (for example Aston New Town); Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 34 pages (for example Bradford).

Sodium

Sodium occurs naturally in water. Levels can also be higher in water from a household ion-exchange softener, which swaps calcium and magnesium for sodium. The tap-water result is not a measure of your total salt intake.

Legal limit (England): 200 mg/l (as Na). Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

Published sodium results on WaterGrade: Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 34 pages (for example Bradford).

Pesticides

Pesticides used on farmland, roadsides and gardens can wash into rivers and groundwater. Suppliers test for the substances likely to be used in each catchment and remove them in treatment where needed. DWI explains that the 0.1 µg/l limit for most individual pesticides is not a health-based standard: it dates from a 1980 European limit that reflected what laboratories could measure at the time. The stricter limits for four banned pesticides are health-based.

Legal limit (England): 0.1 µg/l for each individual pesticide (0.03 µg/l for aldrin, dieldrin, heptachlor and heptachlor epoxide) and 0.5 µg/l for total pesticides. Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

WaterGrade counts a place below only when its report includes a total or combined pesticides result. Reports may list individual pesticides separately.

Published pesticides results on WaterGrade: Affinity Water, 813 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); Thames Water, 229 pages (for example Walworth); Yorkshire Water, 34 pages (for example Bradford); United Utilities, 33 pages (for example Lancaster).

Trihalomethanes (THMs)

Trihalomethanes form when chlorine reacts with natural organic matter, such as material from peat or decaying plants. They are called disinfection by-products. Suppliers control them by removing organic matter before disinfection.

Legal limit (England): 100 µg/l for total trihalomethanes. Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

Published trihalomethanes results on WaterGrade: Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 34 pages (for example Bradford).

Other metals

Suppliers also test for metals that can come from the ground, from treatment or from pipes and fittings. A historical area result cannot diagnose a metallic taste or discolouration at your tap today. Why tap water can taste metallic · Brown or orange water

Legal limits from the Water Supply (Water Quality) Regulations 2016, Schedule 1 (England).

Published iron results on WaterGrade: Severn Trent Water, 1,357 pages (for example Aston New Town); Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Wessex Water, 404 pages (for example Cranmore); United Utilities, 62 pages (for example Lancaster); Yorkshire Water, 34 pages (for example Bradford).

Published copper results on WaterGrade: Thames Water, 1,066 pages (for example Walworth); Affinity Water, 813 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 34 pages (for example Bradford).

Each town page lists every metal its supplier report includes, with units and, where published, sample details.

Bacteria checks: E. coli, coliforms and enterococci

Suppliers test for “indicator” bacteria. A detection is a signal that something may have got into the water or the sample, and the supplier investigates it. E. coli and enterococci are indicators of possible faecal contamination. Coliform bacteria are a wider group used to check that treatment and the network are working as they should.

Legal limit (England): none of these bacteria should be found in a 100 ml sample. In legal terms: E. coli and enterococci 0 per 100 ml at consumers’ taps; coliform bacteria 0 per 100 ml in water leaving treatment works and in service reservoirs (95% of each reservoir’s samples must comply), and an “indicator” at consumers’ taps (Schedule 2). Source: Water Supply (Water Quality) Regulations 2016, Schedule 1.

If your supplier issues a boil-water or do-not-drink notice, follow it. An annual result cannot tell you about a problem today.

Published E. coli results on WaterGrade: Affinity Water, 789 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 32 pages (for example Bradford).

Published enterococci results on WaterGrade: Affinity Water, 813 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 34 pages (for example Bradford).

Published coliform bacteria results on WaterGrade: Affinity Water, 686 pages (for example Edgware); Severn Trent Water, 339 pages (for example Ansley Common); United Utilities, 62 pages (for example Lancaster); Wessex Water, 55 pages (for example Bath); Yorkshire Water, 24 pages (for example Doncaster).

PFAS (“forever chemicals”)

WaterGrade holds no PFAS results for any area. PFAS are a large group of man-made chemicals that break down very slowly. The Drinking Water Inspectorate (DWI) requires water companies in England and Wales to monitor for them and act where levels are found. Read our PFAS guide for what is monitored and where results are published.