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tapwater.uk

Where Our Data Comes From

TapWater.uk uses two layers of publicly available water quality data. We do not collect our own samples or conduct laboratory analysis. This page explains exactly where our data comes from and what it does (and doesn't) tell you.

Layer 1: Drinking Water Quality Tests (Primary)

Real tap water — sampled from kitchen taps across the UK

This is actual drinking water quality data from your water company, published through the Stream Water Data Portal. These results are from samples taken at household taps — what you actually drink.

The Stream Water Data Portal is a collaborative initiative where UK water companies publish their drinking water quality test results. Currently, 16 of 18 major water companies participate, including Yorkshire Water, Severn Trent, United Utilities, Anglian Water, Southern Water, and others.

Stream data includes 121+ regulated parameters tested by the Drinking Water Inspectorate (DWI): metals (lead, arsenic, copper), disinfection byproducts (trihalomethanes, bromate), nutrients (nitrate, nitrite, fluoride), pesticides, microbiological indicators (E. coli, coliforms), and physical properties (turbidity, colour, pH). Results are mapped to Lower Super Output Areas (LSOAs), which we link to postcode districts using the ONS National Statistics Postcode Lookup.

Where Stream data is available, it drives your postcode's safety score. These pages show a green Drinking water quality data badge.

Layer 2: Environmental Water Monitoring (Supplementary)

Rivers, groundwater and reservoirs — not treated tap water

The Environment Agency monitors the raw water sources that feed into treatment works. This data is shown separately on postcode pages and clearly labelled as environmental monitoring.

The Environment Agency (EA) operates one of the most extensive environmental water monitoring networks in Europe. Their open data API provides access to millions of water quality observations from rivers, lakes, reservoirs, and groundwater boreholes in England.

EA data includes metals, nutrients, physical parameters, and PFAS monitoring. For postcodes where Stream drinking water data isn't yet available, EA data provides the primary score with an amber Environmental monitoring only badge.

Geographic Mapping

We use the ONS National Statistics Postcode Lookup to map every UK postcode to its LSOA (Lower Super Output Area), which links to Stream drinking water data. For EA data, we use postcodes.io to resolve postcodes to geographic coordinates and find nearby monitoring points.

Update Frequency

Our data pipeline runs automatically on a daily schedule:

  • Stream Water Data Portal— water companies publish annual datasets. We fetch the most recent year's data for each company daily.
  • EA Water Quality API — queried daily for each covered postcode area. New observations are incorporated automatically.
  • LSOA mappings — updated when the ONS publishes new postcode lookup data (typically quarterly).

Coverage

Stream drinking water data is currently available from: Yorkshire Water, Severn Trent, United Utilities, Anglian Water, Southern Water, South West Water, Portsmouth Water, Welsh Water, and Northumbrian Water. Thames Water, Wessex Water, and Bristol Water are not yet on the portal — postcodes in those areas use EA environmental data only.

We cover 220 postcode districts across England, Wales, and parts of Scotland, with more being added as water companies publish additional data.

Open Data Commitment

All data used by TapWater.uk is published under open licences and is freely available to anyone. We do not claim ownership of any underlying data. Our value is in combining, scoring, and presenting this information in a way that's useful to real people — not in the data itself.

Sources: Stream Water Data Portal, EA Water Quality API, ONS Open Geography Portal.