How the data works
The map brings several public records together. Annual results, recent monitor reports and bathing-water evidence answer different questions.
How to read one outlet page
- 1. Check the yearSpills and hours refer to a calendar year.
- 2. Check coverageLow monitor operation makes comparison less reliable.
- 3. Check the report timeRecent status can be delayed or unavailable.
Keep missing values unknown
A blank or unusable source value is shown as unknown. A reported zero stays zero. Missing years are not filled with zero.
Match the same outlet across years
We first use the source ID. If an older year has no matching ID, the company, permit and activity must identify one record in both years. Where both years have coordinates, we reject matches more than 1 km apart. The 2020 return has no grid references for this check.
Keep dates separate
Annual figures have a reporting year. Recent status has a provider update time and a last successful check.
Check recent-report links
We require an exact supplier ID and a location check before we attach a recent report. An unclear match stays unavailable. The 1 km check is a rejection limit, not a claim that the positions are exact.
Show location limits
We convert source grid references for the map. Some source cells list several points; the outlet page says when it uses the first point.
Explain nearby groups
Area pages use 10 km around an ONS place point. Bathing pages use 3 km around a sample point. Both are straight-line searches, not pollution paths.
Use source-listed waterbodies
Water pages group the names and IDs supplied in the annual return. The IDs pass a format check, not a separate river-register check.
Annual totals and corrections
The checked 2025 records contain 292,119 spills. This matches the revised summary workbook. The row durations differ from the summary by about 6.4 minutes across the full dataset. We keep the row values and do not adjust them.
Adding outlet hours can count events that happened at the same time. The result is recorded outlet-hours. It is not the number of hours when a whole river was polluted.
How spills are countedWhat these records cannot tell you
Monitor records do not show discharge volume, bacteria levels, legal compliance, public access or whether water is safe. A stopped or missing report is not a clean-water result.