Ireland Reservoir Transparency

Water level data (in metres above ordnance datum) is publicly available in near-real-time through waterlevel.ie for ~380 stations including the ~30 lake and reservoir stations in the covered subset. ESB publishes daily PDF charts of water levels for Poulaphouca (Liffey), Shannon (Lough Derg/Ree), Lee, and Erne systems via esbhydro.ie. However, no agency publishes reservoir storage as volume or percentage-full — the universally useful metric for water supply management. Uisce Éireann's open data portal lists a 'Reservoirs' dataset but it contains only infrastructure location data (XLSX), not operational storage levels. There is no national reservoir storage dashboard analogous to Spain's MITECO or the US USGS NWIS.

OPW waterlevel.ie provides a documented, machine-readable REST-style API (CSV and GeoJSON endpoints at http://waterlevel.ie/page/api/) under CC BY 4.0. Data for the covered reservoirs updates every ~15 minutes. However, the API exposes only water level in metres — not reservoir storage volume or percentage. The 5-week rolling window on the main API means long-term programmatic access requires a separate portal (Hydro-Data). ESB data is available only as PDFs, not machine-readable. Uisce Éireann open data is XLSX-only static download with no API. EPA HydroNet (WISKI) supports downloads but no documented REST API for external use.

v1.3.0 capacity-weighted methodology applied 2026-05-29. Ireland total national reservoir storage capacity ~500 hm³ across ~50 reservoirs and regulated lakes combining ESB hydropower impoundments (Poulaphouca/Blessington dominant, plus Lough Derg/Ree on the Shannon, Inniscarra/Carrigadrohid on the Lee, Erne system) with Uisce Éireann drinking-water reservoirs (Vartry, Roundwood, Stillorgan, Cloosh and regional supply impoundments). COVERED capacity ≈ 350 hm³ via OPW EPA HydroNet (WISKI) + waterlevel.ie REST API (~30 reservoir/lake-level stations including Poulaphouca, Lough Derg, Lough Ree, Inniscarra) + ESB daily PDF charts for the Liffey, Shannon, Lee and Erne hydropower systems. coverage = round(100 × 350 / 500) = 70. The covered subset captures the strategic hydropower and Dublin supply reservoirs; smaller regional supply impoundments remain unpublished.

Scoped to the 30 covered reservoirs, OPW's National Hydrometric Archive covers over 70 years for the oldest gauges, with data collection starting in the early 1940s. Digitally accessible processed flow records are most reliable from the early 1970s onward (~55 years) for most covered stations. The Hydro-Data portal (waterlevel.ie/hydro-data) provides quality-assessed water level and flow records from both active and inactive stations going back decades. ESB's hydropower reservoir level archive extends multi-decade. The median historical depth across the 30 covered reservoirs is approximately 55 years. The limitation: the historical archive covers water level/flow, not reservoir storage volume.

OPW waterlevel.ie updates water level data approximately every 15 minutes from data loggers at the ~30 reservoir stations in the covered subset — excellent frequency. ESB publishes daily PDF charts for its reservoir/river systems (Liffey, Shannon, Lee, Erne). EPA publishes monthly Hydrology Summary Bulletins. Uisce Éireann's open data is static XLSX, updated infrequently. The high-frequency updating applies only to OPW's stage (water level in metres) data, not to any reservoir storage volume or percentage metric.

OPW publishes station metadata (coordinates, reference numbers) in GeoJSON for the covered reservoir stations and explains sensor types and data encoding. Data is flagged as provisional/unchecked on the real-time feed, with quality-assessed data in the archive. However, no stage-to-volume conversion curves or reservoir capacity tables are published, so users cannot derive storage percentage from the water level data without independent bathymetric data. Uisce Éireann references a 'standardised methodology' for its capacity register but does not publish it. ESB provides no methodology documentation for its PDF charts.

Ireland is an English-speaking country. All portals — waterlevel.ie, water.ie, epa.ie, esb.ie, data.gov.ie — operate exclusively in English. All documentation, APIs, metadata, and bulletins are in English. No translation barrier exists for any international user.