Every free hydrology dataset with an API
By Chris Cameron-Hann · Published
A registry-scoped tour of open hydrometry, rainfall, flood and water context APIs, including the awkward access and licence distinctions.
Free is a slippery word in a consultancy. Sometimes it means you can send a request without a key. Sometimes it means the data has an open licence. Sometimes it means a personal experiment is allowed while paid client work needs a subscription. Before we get enthusiastic about a new water API, it is worth deciding which of those meanings we need. Otherwise the supposedly free integration can become a surprisingly expensive assumption.
This is a tour of the hydrology and flood data_api records in TerraMCP's data/listings.json snapshot on 15 October 2026. “Every” means that bounded registry collection, with related water context included and overlapping records called out. It is not a claim to have found every service on Earth. I separate entries with explicit free-access evidence from entries merely recorded as keyless or openly licensed. Where the registry is silent on price, quotas or commercial use, so am I.
The most clearly evidenced free starting points
For England, the EA Flood Monitoring API explicitly records free open access without authentication or registration, with Open Government Licence 3.0 and attribution requested. Its description covers flood warnings, river levels, rainfall and monitoring-station observations. The EA Hydrology API also records free access and no authentication, with the same named licence. Its emphasis is station metadata and quality-labelled flow, level, groundwater and rainfall time series.
These are distinct service choices, even if a project uses both. I would use the registry descriptions to shortlist Flood Monitoring for current context and Hydrology for historical series investigation. That is a proposed workflow, rather than a guarantee that every desired parameter exists at every station. First discover the station and series, then inspect availability, then decide whether the data fits your question. Fetching a huge table before checking those basics rarely saves time.
NRFA Data API explicitly records free access with no API key or authentication currently, governed by NRFA Data Terms and Conditions. The parallel NRFA API record describes UK daily flows, catchment rainfall, peak flows and catchment metadata. Count the family once when estimating your sources. Its own terms remain important: an easy request is not permission to relabel the output as unrestricted public-domain material.
The USGS Water Data API has another useful explicit access statement: free to use, with an optional API key for higher rate limits. Its description concerns US water observations and monitoring-location metadata. However, the same access enrichment says the licence is not stated. That combination is perfectly possible. I would shortlist it for a US hydrometry task, while leaving the downstream reuse check visibly open until the relevant terms have been established.
British services with conditions and overlapping entries
The SEPA Time Series API describes Scottish level, flow and rainfall through KiWIS, with no key for normal access and a key for bulk access. SEPA KiWIS Time Series API records the same important normal-versus-large-volume distinction. Both name Open Government Licence 3.0 in their respective wording. Treat them as overlapping catalogue entries, and investigate the bulk access route before writing a downloader that assumes unlimited anonymous throughput.
The separate EA Rainfall API record describes recent rainfall at gauges, with auth recorded as none and licence OGL-3.0. Because its name places it within Flood Monitoring, I would investigate it as a route into that service family, rather than announcing an independent rainfall network. That distinction helps you avoid creating three connectors where one carefully designed source adapter would do.
Welsh hydrometry needs a different conversation. NRW River Levels and NRW API Portal describe river levels and warnings, but both record API-key access and OGL-3.0. The registry does not establish the price of that access. Keys do not prove that a service costs money, and open licences do not prove that every delivery mechanism is free. These are conditional leads, not members of an evidenced anonymous-free shortlist.
Irish and continental European water observations
OPW Waterlevel.ie describes Irish river levels; EPA Ireland Geoportal / Hydronet describes Irish water quality. Both records list no authentication and CC-BY-4.0. These look like useful starting points for their named purposes. They are different kinds of evidence, though: water quality is not a substitute for discharge, and neither description establishes a complete record at your chosen location. Read the station or dataset metadata before promising a deliverable.
For continental Europe, the registry lists PEGELONLINE for German waterway levels under DL-DE-Zero-2.0, Hub'Eau for French flow under Licence Ouverte 2.0, and Vigicrues for French flood vigilance under Licence Ouverte. All three record authentication as none. That is a useful set of discovery leads, but the descriptions are brief. I would not infer update intervals, station counts or historical coverage from those short labels.
Rijkswaterstaat Waterinfo / DDL describes Dutch water levels, with no authentication and CC0 recorded. SMHI Open Data describes Swedish observations and hydrology, with no authentication and CC-BY-4.0. NVE HydAPI describes Norwegian discharge under NLOD but requires an API key. Keep NVE in the investigation list, with access cost unresolved. A tidy continental map of provider names would be attractive, but these records do not establish comparable coverage between countries.
North America and Australia
Alongside the modern USGS water API, USGS NWIS Instantaneous Values is described as real-time streamflow, with no authentication and public-domain licensing recorded. USGS StreamStats is described as watershed delineation under the same access and licence labels. They answer different questions. A delineated catchment can support an investigation, but it is not a measured hydrograph. Decide which output your method needs before selecting the easier endpoint.
NOAA National Water Model / NWPS describes US river forecasts, with no authentication and public-domain licensing. NOAA CO-OPS Tides and Currents API describes coastal levels, tide predictions and currents. CO-OPS has null authentication and licence fields, and its access enrichment explicitly says those details are unverified. It belongs in a water-data investigation, but I cannot honestly sell it as proven free commercial access from this registry alone.
For Canada, MSC GeoMet describes Canadian hydrometric data under ECCC Open Licence, while ECCC Hydrometric / HYDAT describes Canadian river flow under OGL-Canada. Both list no authentication. For Australia, BOM Water Data Online describes river flow under CC-BY-4.0, also without authentication. These provide regional starting points, not a justification for assuming identical units, quality codes or data models across providers.
Forecasts, satellite water and global discovery
The Open-Meteo Flood API record describes river discharge forecasts at a point and lists no authentication with CC-BY-4.0. The separate Open-Meteo API record explicitly limits its free keyless service to non-commercial use and says commercial subscriptions are separate. Do not transfer a free-service assumption between related records. A consultant should establish the specific product's service terms before putting a forecast request into a paid workflow.
GloFAS is described as global flood awareness, with no authentication and a Copernicus licence recorded. Copernicus Emergency Management Service Rapid Mapping describes flood extent activation, again with no authentication and a Copernicus licence. Their short registry descriptions do not establish identical access mechanisms or outputs. I would distinguish the awareness product from an event extent product in the source register, and verify the actual dataset before planning an extraction.
JRC Global Surface Water describes water occurrence with no authentication and CC-BY-4.0. Digital Earth Australia describes water observations from space with the same access and licence labels. These are useful contextual leads when the question concerns spatial water observations. They do not become gauged discharge simply because both are filed under a water theme. WMO WHOS describes global hydrometric services but lists the licence as Various, so carry provider-level terms into any follow-on investigation.
Related water evidence that deserves a separate drawer
The registry's hydrology and flood categories also contain services useful around the edges of an investigation. EA Catchment Data Explorer describes WFD waterbody status; the EA groundwater abstraction licences register describes abstraction licences near a site. Both record no authentication and OGL-3.0. GSI data describes Irish boreholes under CC-BY-4.0 with no authentication. These are context records, not interchangeable measurement archives.
Mapping leads include the Defra platform, SEPA Flood Maps and DataMapWales, all recorded with no authentication and OGL-3.0. FEMA's National Flood Hazard Layer describes US flood zones, with no authentication and public-domain licensing. Géorisques describes natural risks at commune level, under Licence Ouverte with no authentication. These can support spatial screening; the descriptions do not make them hydrometric time series.
EMODnet is listed for bathymetry with Various open licences; OBIS API for marine species with CC per dataset. Both list no authentication. The Australian Rainfall & Runoff Data Hub describes ARR design flood inputs under CC-BY, also without authentication. Preserve those per-product distinctions. Meanwhile, Ambiental FloodScore is explicitly commercial and licence-based, so it is excluded from the free shortlist rather than quietly bundled with the public services.
Turning the list into a working data plan
There are two other tempting names to handle carefully: GRDC and HydroSHEDS. The registry classifies both as datasets, not data_api entries. GRDC describes river discharge with access subject to station or data terms; HydroSHEDS describes basins, rivers and drainage products. Neither record establishes the free API claim this article is investigating. Keep them as related resources, rather than inventing an endpoint to make the headline feel more comprehensive.
My practical selection order is geography, quantity, observation versus forecast or mapping, available period, terms, then retrieval mechanics. For each chosen source, save the documentation link, request details, identifiers, access date and raw response. Check whether empty results indicate no observations, a failed filter or an incomplete page. That small habit turns a long provider list into something a colleague can review and repeat. Free access is useful; a clear account of what you downloaded and why is what makes it useful on a project.