What's in UK tap water?

No UK legal limit

Man-made chemicals that don't break down. Linked to cancer, immune disruption, and thyroid problems. The UK has no legal limit despite EU and WHO guidelines.

UK limit: 0.01 mg/L

Neurotoxin with no safe exposure level. Mainly from old pipes in pre-1970 homes. Affects children's cognitive development even at low levels.

UK limit: 0.1 mg/L

Disinfection byproducts formed when chlorine reacts with organic matter. Linked to bladder cancer risk. Higher in areas using surface water.

UK limit: 50 mg/L

From agricultural fertiliser runoff. Dangerous for infants under 3 months (blue baby syndrome). Elevated in farming regions.

Zero tolerance

Indicator of faecal contamination. Any detection in treated water triggers immediate investigation. UK regulation requires zero presence.

UK limit: 1.5 mg/L

Added to ~10% of English water supplies. Prevents tooth decay but excess causes dental fluorosis. Naturally present in some regions.

UK limit: 5 mg/L (residual)

Added as disinfectant to kill bacteria. Safe at UK levels but creates byproducts (THMs). Can affect taste and smell.

UK limit: 2 mg/L

Mainly from copper plumbing. High levels cause nausea and stomach cramps. More common in new-build properties with soft water.

UK limit: 0.01 mg/L

Group 1 carcinogen found naturally in groundwater, especially in Cornwall and Devon. Linked to skin, bladder and lung cancers.

UK limit: 0.05 mg/L

Common cause of brown/black water. Neurological effects in infants at elevated levels. WHO lowered guideline in 2022.

UK limit: 0.2 mg/L

Most common cause of brown/orange water. From aging cast iron mains. Aesthetic standard rather than health-based limit.

UK limit: 0.001 mg/L

Potent neurotoxin damaging the nervous system and kidneys. UK limit is six times stricter than the WHO guideline.

UK limit: 0.1 µg/L each

Agricultural chemicals including metaldehyde, clopyralid and MCPA. One of the most common causes of regulatory failures.

No UK limit set

Emerging contaminant from textiles, tyres and plastic breakdown. No regulatory limit yet. EU will require monitoring from 2026.

UK limit: 0.5 mg/L

More toxic than nitrate. Can form in distribution pipes. Poses blue baby syndrome risk to infants under three months.

UK limit: 4 NTU

Water cloudiness that shields bacteria from disinfection. Not harmful itself but indicates possible treatment problems.

UK limit: 0.2 mg/L

From aluminium sulphate used in water treatment. Debated but inconclusive link to Alzheimer's disease.

Zero tolerance

Indicator bacteria with zero-tolerance policy. Detection signals possible treatment failure and triggers immediate investigation.

UK limit: 0.005 mg/L

Group 1 carcinogen that accumulates in the kidneys. Can leach from galvanised pipes. Causes bone demineralisation.

UK limit: 0.05 mg/L

Hexavalent form is carcinogenic. EU tightening limit to 0.025 mg/L from 2036. From chrome plating and leather tanning.