Data sources
We check that each source can be used, updates reliably and gives the information its forecast needs. Early previews are clearly labelled. Only sources that pass these checks can drive a live forecast.
Latest connections
SEPA river readings and the Stream catalogue now join the three previously connected official sources. Welsh Water and Wessex Water are early previews collected from their public pages. 3 sources are still not connected: one needs an NRW access key, while 2 depend on information that is not public. Checked 14 Aug 2026.
How public information is used
Otter uses factual readings and status information, with a link to the publisher. It does not copy articles, charts, images or whole pages. If a source explicitly forbids the way Otter needs to use it, that source and any forecast depending on it are removed.
Early preview data
These readings come directly from public water-company pages. They may be incomplete or stop working if a page changes. They do not necessarily describe the whole local supply and do not predict restrictions. Always follow the company’s official notice.
The published TOTALS row covers the Wrexham reservoir system. Llyn Clywedog is explicitly excluded because the supplier says it is not used directly to supply its customers.
Open official sourceFour supplier reservoirs are parsed separately. No supplier-wide or Water Resource Zone total is inferred.
Open official sourceThe page supplies monthly regional context. London serving continues to use the separately commissioned weekly EA anchor.
Open official sourceThis is a supplier-wide relative groundwater position, not the undisclosed absolute Well X drought-trigger series.
Open official sourceFour supplier-published Welsh regions are shown as current public context. They are not transferred to the 23 Water Resource Zones without an authoritative supplier relationship table.
Open official sourceSupplier-wide monthly context from a browser-backed public-page collector. Storage, groundwater and stream support remain separate signals and are not presented as an integrated restriction forecast.
Open official source| Publisher and purpose | Status | How often it updates | Usage terms | What Otter uses it for |
|---|---|---|---|---|
| Environment Agency monthly reservoir storage history | in use | P1M | Open Government Licence v3.0 | Named monthly percentage-full markers are extracted from the Environment Agency national reservoir map and linked to separate current supplier readings. Ambiguous markers remain null. This source independently replaces, and does not read, the withdrawn UKCEH Monthly Hydrological Summary archive. |
| Environment Agency operational geography | in use | on_revision | Open Government Licence | The source-hashed full download is transformed without simplification into tiled local lookup assets; the live OGC service is fallback-only and a simplified copy is used only for the public map. |
| Ofwat appointed water company boundaries | being reviewed | on_revision | Open Government Licence | Reference layer for appointed-company areas; the legal appointments and variations remain definitive. |
| Ofwat new appointments and variations | in use | event_driven | Open Government Licence | The current XLSX is downloaded and its columns, sequential records and dates are validated. It identifies 2,635 NAV sites, but it does not include postcode-ready legal boundary geometry, so postcode lookup still uses incumbent areas and states that limitation. |
| Drinking Water Inspectorate england drinking water company register | being reviewed | P1Y | Open Government Licence | Authoritative 2025 count of 24 reporting drinking-water companies, including nine inset appointees. |
| postcodes.io / Office for National Statistics postcode geocoding | in use | on_directory_update | Open Government Licence derived data | Production replacement should load the ONS Postcode Directory directly. |
| Office for National Statistics via Nomis small area population | in use | on_revision | Open Government Licence | Source-hashed TS001 Output Area usual-resident totals provide the denominator and weights for the resident-weighted WRZ numerical-coverage measure. |
| Office for National Statistics small area population geography | in use | on_revision | Open Government Licence | All 188,880 centroids are source-counted and normalised-hashed before English Output Area residents are assigned to exact official WRZ polygons. |
| Water UK official restriction index | in use | P1D | link_only | National discovery and cross-check source; supplier notices remain authoritative. |
| South West Water official restriction postcode scope | in use | request_time | publisher_terms_review_required | The supplier's public restriction page calls this same-domain boolean endpoint. Otter uses a loopback-only host bridge because the local Worker runtime cannot complete the supplier TLS request; successful answers are cached for five minutes and failures preserve supplier confirmation. |
| Dŵr Cymru Welsh Water official restriction postcode scope | in use | request_time | publisher_terms_review_required | The supplier's public restriction page calls this same-origin JSON endpoint with a page-specific panel ID. Its JavaScript WAF rejects server fetches, so the loopback-only bridge discovers the current panel in an isolated headless browser, validates an exact postcode match, caches only the boolean for five minutes, and preserves supplier confirmation on failure. |
| Environment Agency river groundwater rainfall | in use | P1D | Open Government Licence | Qualified EA histories now support Lilley Bottom for Affinity Central, Chipstead for SES, five Cambridge trigger boreholes, Wolverton for Affinity Southeast, Woodyates for Wessex, and supplier-mapped Southern Water Chalk indicators. Four named River Test gauges also reconstruct Total Test Flow. Fresh current observations remain visible even when every forecast horizon is withheld; projections publish only after independent gates pass. |
| Environment Agency weekly drought context | in use | P7D | Open Government Licence | The current year collection is parsed for its newest dated report and page-update timestamp with fixture coverage and a 12-day freshness gate. It is regulatory drought context, not a reservoir or aquifer level. |
| Environment Agency monthly reservoir storage maps | in use | P1M | Open Government Licence | Named markers are extracted from 126 monthly maps from 2016 onward and ambiguous values remain null. Two withdrawn 2019 Blithfield reports have explicit filename-bound source-audit corrections because the withdrawal watermark crossed the marker; rejected OCR values remain in lineage. The archive supports the published Essex pair and SES Bough Beech component; Blithfield remains research-only because all three held-out horizons fail. |
| Natural Resources Wales river groundwater rainfall | not connected | P1D | Open Government Licence v3 | The licence is confirmed. Reliable API use requires registration and a key, and an authoritative station-to-supply-area mapping is still needed before observations can drive customer results. |
| Scottish Environment Protection Agency river groundwater rainfall | in use | P1D | Open Government Licence v3 | Anonymous low-volume queries now validate the public station catalogue, all daily groundwater series and their latest quality-coded values. The measurements are geographic hydrometry context only because Scottish Water has not published authoritative station-to-supply-system relationships. |
| Met Office deterministic weather forcing | early preview | P1D | Met Office Weather DataHub licence | The nationwide UKV order delivers one complete 15:00 UTC run daily under the Weather DataHub application licence. The local decoder retains a bounded 690-cell England-and-Wales mesh for postcode garden guidance and a separate Yorkshire reservoir-model public preview; both fail closed after 36 hours, the mesh cannot promote reservoir forecasts, and raw-data redistribution remains disabled. Powered by Met Office data. |
| Met Office historical weather calibration | early preview | P1M | Open Government Licence | Provisional 12 km rainfall and temperature fields are area-averaged over the Yorkshire pilot box for calibration and held-out testing. |
| Yorkshire Water demand rainfall river status context | early preview | P1M | public factual observations with attribution | Monthly demand, rainfall and river status are displayed as operational context and are not yet fitted model inputs. |
| UK Centre for Ecology & Hydrology reservoir metadata and waterbody geometry | in use | on_revision | Open Government Licence v3.0 | The OGL reservoir inventory and matching OGL waterbody geometry support the national map and topographic catchments. They are distinct from the withdrawn Monthly Hydrological Summary history and are not a substitute for operational supply relationships. |
| Cambridge Water groundwater trigger geography | in use | on_revision | link_only | Names the five drought-trigger boreholes used in the one-zone Cambridge seasonal-index baseline. Live absolute observations come independently from the EA hydrology API. |
| Portsmouth Water groundwater trigger method | not connected | on_revision | link_only | Establishes the primary 80-plus-year Well X indicator and the exact blocker: its identity and absolute history are not public, while named EA sites are supporting checks only. |
| Wessex Water future reservoir level feed | not connected | on_revision | link_only | The public schedule lists the wider Wessex Water Reservoir Levels stream for March 2027. Until an independently reusable reservoir history is available, the published Wessex numerical outlook is limited to the separately sourced Woodyates groundwater indicator. |
| South East Water daily distribution input history | being reviewed | historical_only | South East Water Open Data Licence | The public series covers 2023 only. It explains the fast-demand feature but cannot validate a continuous 2024-26 operational arm. |
| Environment Agency long term supply demand context | in use | on_revision | Open Government Licence | The dataset metadata, OGL statement, public-access statement and current XLSB download are validated automatically. This is long-term planning context only and is never treated as a live reservoir or aquifer observation. |
| Stream source discovery catalogue | in use | P7D | catalogue_terms_review_required | The ArcGIS catalogue is paginated and structurally validated for source discovery. It is not treated as one hydrological feed: each selected dataset retains separate licence, freshness, geography and modelling gates. |
| Yorkshire Water reservoir storage | in use | P7D | CC BY 4.0 | Annual 2022 onward layers are merged and validated for the supplier-wide Yorkshire baseline. The current ArcGIS item explicitly publishes a CC BY 4.0 licence; attribution remains attached. Reservoir-to-small-operational-system relationships are not inferred. |
| Greater London Authority / Thames Water reservoir storage history | in use | P1M | Open Government Licence v2 | Daily Lower Thames and Lower Lee percentages from 1989 provide the commissioned history for the London Water Resource Zone baseline; current serving uses the separate weekly Environment Agency anchor. |
| Environment Agency reservoir storage current | in use | P7D | Open Government Licence v3 | Official weekly chart reports Lower Thames and Lower Lee group storage. The two values are capacity-weighted only for the London Water Resource Zone current anchor. |
| Affinity Water groundwater resource position | in use | P1M | public factual observations with attribution | Supplier drought-planning context maps EA Lilley Bottom to Central and Wolverton to Southeast. Passing Central 14- and 60-day and Southeast 90-day-equivalent horizons are published. East remains blocked because the Lady Lane public series ends in 2020; the restriction-warning replay remains research-only. |
| Anglian Water mixed resource position | in use | P1M | public factual observations with attribution | Current Grafham, Pitsford and Rutland readings remain attributed facts. The official East England regional trace directly includes Grafham and Rutland and its 30-day-equivalent horizon passes the unchanged held-out gate for the Ruthamford North and South indicator; it remains broader than Anglian Water and does not represent Pitsford or the complete operating system. |
| Dŵr Cymru Welsh Water reservoir and status | early preview | P7D | public factual observations with attribution | A browser-backed collector downloads and OCR-validates the supplier's weekly bulletin for North West, North East, South West and South East Wales. These four public regions remain context only until the supplier publishes authoritative relationships to its 23 Water Resource Zones. |
| Hafren Dyfrdwy reservoir storage | early preview | P7D | public factual observations with attribution | A private source-specific parser reads the dated Wrexham-system TOTALS row and explicitly excludes Llyn Clywedog, which the supplier says is not used directly for its customers. Zone mapping and repeated live reliability remain to be validated. |
| Northumbrian Water reservoir storage | in use | P1M | public factual observations with attribution | Current Northumberland, Weardale and Teesdale groups remain attributed facts. The direct Kielder history passes at 60 and 90 days for the Kielder WRZ indicator; the failed 30-day horizon and the separate Berwick-Fowberry groundwater zone remain withheld. |
| Essex & Suffolk Water mixed resource position | in use | P1M | public factual observations with attribution | The current combined Hanningfield and Abberton value anchors an official Environment Agency map-derived history weighted by the supplier's published reservoir capacities. Publication, when a held-out horizon passes, is confined to the Essex WRZ; the three Suffolk zones are not represented. |
| Severn Trent Water reservoir storage | in use | P7D | public factual observations with attribution | The dated TOTALS rows provide a 164-week definition-audited Strategic Grid history. Its held-out 14-day and four-week horizons remain the headline result; the replacement Environment Agency archive adds separately gated Derwent Valley monthly horizons for the Strategic Grid and Nottinghamshire. Clywedog fails every replacement gate. |
| Southern Water reservoir storage | early preview | P7D | public factual observations with attribution | A source-specific parser now reads the four official weekly reservoir charts without combining them. Bewl remains the separately evidenced reservoir component for both Kent Medway zones; the values are a public preview until repeated runs and source-revision checks pass. |
| South West Water reservoir storage | in use | P7D | public factual observations with attribution | Roadford's current supplier chart anchors its 90-day indicator; Stithians supplies all three Colliford-zone monthly horizons; and the official South-west England regional trace supplies a passing 30-day Wimbleball-zone indicator. Direct Colliford and Wimbleball models remain failed results. |
| Bristol Water reservoir storage | in use | P7D | public factual observations with attribution | The dated Blagdon reading anchors the Bristol WRZ's separately scoped 30-day-equivalent reservoir indicator. The 60- and 90-day gates fail, and the indicator does not claim to represent the other reservoirs, canal imports, groundwater or operating state. |
| Thames Water reservoir and rainfall | early preview | P1M | public factual observations with attribution | A private parser reads the supplier's monthly London, West London, Lee Valley and Farmoor context. London serving continues to use the separately commissioned weekly EA anchor; Farmoor-to-zone mapping remains under review. |
| United Utilities reservoir storage | in use | P7D | public factual observations with attribution | Current regional and source-group values remain attributed facts. The official north-west regional reservoir chart supplies independently passing 30-, 60- and 90-day-equivalent Strategic WRZ indicator horizons. |
| Wessex Water mixed resource position | early preview | P1M | public factual observations with attribution | A browser-backed public preview now reads the supplier's monthly total surface-reservoir percentage, rainfall position, qualitative groundwater status and dated stream-support list. These remain context beside the separately commissioned Woodyates and Clatworthy indicators, not an integrated restriction forecast. |
| Portsmouth Water groundwater resource position | early preview | P1M | public factual observations with attribution | A private parser reads the dated supplier-wide groundwater departure from average, rainfall position and drought-plan status. It does not substitute this relative measure for the undisclosed absolute Well X drought trigger. |
| South East Water mixed resource position | in use | P7D | public factual observations with attribution | The dated Ardingly observation anchors the published Haywards Heath level horizons; Arlington is retained as uncommissioned context. |
| South Staffs Water mixed resource position | in use | P7D | public factual observations with attribution | Configured for commissioning; not used for public numerical values. |
| Cambridge Water groundwater resource position | in use | P7D | public factual observations with attribution | Supplier drought-planning evidence identifies five trigger boreholes for the one Cambridge WRZ. Current levels come from the commissioned EA hydrology archive; 30- and 90-day-equivalent seasonal-index horizons pass. |
| SES Water mixed resource position | in use | P1M | public factual observations with attribution | The supplier's current mixed-resource page and WRMP define the single zone and 85% groundwater share. The EA Chipstead archive supplies the primary Chalk-reference trajectory; 125 unambiguous monthly Bough Beech markers supply a separately gated surface-water component. Redhill rainfall remains a research-only antecedent filter, and Lower Greensand is still outside the published indicators. |
| Scottish Water regional resource position | in use | P14D | public factual observations with attribution | Scotland-wide storage is served as a broad observed resource state; four public regions are not claimed as customer supply polygons. |
