Data for the public interest

Lead contamination remains one of the UK's most persistent drinking water challenges. TapWater.uk analysis of water company compliance data reveals that DA5 recorded lead at 6.4x the legal limit of 0.01 mg/L in its most recent sample.

The UK tightened its legal limit for lead in drinking water from 0.025 to 0.01 mg/L in 2013 to align with WHO guidelines. An estimated 40% of UK homes still have lead service pipes, and there is no safe level of lead exposure — even low doses are linked to developmental effects in children.

Based on water company compliance testing published via the Stream Water Data Portal, covering 1,942 UK postcode districts with drinking water results sampled in the last three years. Districts with fewer than five measured parameters, or with only environmental river and groundwater monitoring, are excluded. Uses the most recent sample for each district.

Data last refreshed: 2026-08-20

High nitrate levels in drinking water are a growing concern in UK agricultural regions, where fertiliser runoff leaches into groundwater sources. TapWater.uk analysis shows TF7 recording nitrate at 91% of the UK legal limit of 50 mg/L in its most recent sample.

The UK Drinking Water Regulations set a 50 mg/L limit for nitrate, in line with EU standards. Nitrate above this level poses a risk of methaemoglobinaemia — reduced oxygen-carrying capacity in the blood — particularly in infants under six months. Water companies in affected zones must blend or treat supply to maintain compliance.

Based on water company compliance testing published via the Stream Water Data Portal, covering 1,942 UK postcode districts with drinking water results sampled in the last three years. Districts with fewer than five measured parameters, or with only environmental river and groundwater monitoring, are excluded. Uses the most recent sample for each district.

Data last refreshed: 2026-08-20

PFAS — per- and polyfluoroalkyl substances — have contaminated water sources near — more than anywhere else in the UK, with 0 individual compound detections recorded in Environment Agency monitoring data. Unlike most contaminants, PFAS do not break down in the environment or the human body, earning them the name "forever chemicals".

The UK introduced a drinking water standard for PFAS in 2021, setting a 0.1 µg/L limit for individual PFAS compounds and a 1 µg/L sum-of-PFAS limit. The main UK sources are fire-fighting foam at airfields and industrial sites, and agricultural application of contaminated sewage sludge. Long-term PFAS exposure is associated with thyroid disruption, immune suppression, and increased cancer risk.

Based on analysis of Environment Agency Water Quality Archive PFAS monitoring data, aggregated by city water supply zone. Detection counts include any measurement above the laboratory reporting limit.

Data last refreshed: 2026-08-20

Hard water costs UK households an estimated £700m per year in appliance damage, scale build-up, and excess detergent use. At 373 mg/L CaCO₃, HU16 sits in the "very hard" classification — more than four times harder than the softest water areas in Scotland and Wales.

The UK does not set a maximum legal limit for water hardness, though the DWI recommends suppliers keep levels below 200 mg/L for optimal plumbing health. Hardness is determined by the geology of the source catchment — chalk aquifers in South East England and the East Midlands produce the hardest water, while upland reservoirs in the north and west supply naturally soft water.

Based on Drinking Water Inspectorate zonal hardness data, mapped to postcode districts. Values represent total hardness as calcium carbonate equivalent.

Data last refreshed: 2026-08-20

UK tap water quality varies more than most people realise. LL14 leads the country with a safety score of 9.8/10 — consistently low contaminant readings across all 19 tested parameters. At the other end of the table, several postcodes score below 5, with multiple contaminants reading close to or above legal limits.

The UK's Drinking Water Inspectorate reports that 99.96% of tests pass legal standards at the point of measurement — but compliance tests are taken at the treatment works, not the tap. TapWater.uk scores are based on what arrives at household taps, incorporating distribution losses, pipe age, and local geology.

Safety scores combine 19 contaminant readings from Environment Agency and DWI data, normalised against legal limits and weighted by health risk. Scores reflect the most recent annual data for each postcode district.

Data last refreshed: 2026-08-20