CORE
A positive intersection covering at least 1% of the Built Up Area. These zones contribute to headline monitoring figures.
How the data is connected
Methodology
A plain-language guide to how place pages are matched, calculated and presented.
How places are matched to water data
We compare the official Census boundary for a town or city with official Water Supply Zone boundaries from Uisce Éireann. When the areas overlap meaningfully, the zone is used for that place page.
A place can overlap more than one Water Supply Zone. The overlap percentage describes land area only; it is not the percentage of residents or homes supplied by that zone.
How monitoring results are combined
For each mapped Water Supply Zone, we group EPA monitoring records by year and count each source record once. If a place has several included zones, their records are combined for the page totals without duplicating a zone.
Monitoring applies to the Water Supply Zone as a whole. Sampling locations may therefore be outside the settlement shown on the page, and nearby places sharing a zone can show the same zone-wide figures.
What a listed exceedance means
A listed exceedance is a record published in the EPA’s separate exceedance dataset. WaterCheck Ireland reports those records as published and does not create additional exceedances by comparing every result with a limit.
The listed exceedance frequency shown on place pages is a simple descriptive calculation: exceedance records divided by monitoring result records. It is not an official EPA compliance rate or a safety score.
Important limitations
The pages show historical monitoring data, not current conditions at an individual tap. Missing years are shown as unavailable rather than zero, and text results such as “less than” values are preserved without being treated as ordinary numbers.
Zone boundaries and monitoring coverage can change over time. Geographic overlap cannot confirm which supply serves a particular property. For current notices affecting an address or Eircode, check Uisce Éireann.
Technical details
Settlement and Water Supply Zone polygons are reprojected to EPSG:2157 before intersection areas are calculated. All positive intersections are retained for audit, while only the main mapping class contributes to headline monitoring totals.
EDEN Water Supply Zone codes connect the geographic mapping to EPA scheme codes. Source records are grouped directly by these codes so yearly scheme reference rows do not multiply monitoring results.
SECONDARY
A positive intersection covering at least 0.1% but less than 1% of the Built Up Area. It is retained for context and review.
BOUNDARY_TOUCH
A positive intersection below 0.1% of the Built Up Area. It is retained for boundary transparency and does not contribute to headline figures.