SourcesThe data family
waterdata.dev
Free, versioned daily streamflow for every active USGS stream gage and weekly US Drought Monitor categories for every county, covering the last 400 days, with citable URLs.
What it is
waterdata.dev is a free public-data site for US streamflow and drought. It republishes daily stream gage data from the US Geological Survey (USGS) and county drought categories from the US Drought Monitor, as plain files and a simple API with no key or signup. Like this site, it’s run by Eric Ness.
The streamflow comes from the new USGS Water Data APIs. USGS plans to shut down its older WaterServices API on February 22, 2027, and the site offers itself as a stable replacement for scripts written against that one. The drought data comes from the National Drought Mitigation Center at the University of Nebraska-Lincoln, which produces the Drought Monitor with USDA, NOAA and NASA.
What it measures
The site has three datasets, each covering roughly the last 400 days.
- Daily streamflow. Daily mean discharge, in cubic feet per second, at every USGS stream gage that reported one in the last 400 days. Each day is flagged
provisionaluntil USGS approves it, withestimatedandiceflags and the full list of USGS qualifier codes. The site re-reads the whole window every day, because USGS revises provisional values for months. - USGS stream gages. One row per gage in the streamflow data: name, state, county, hydrologic unit, coordinates, drainage area and the first and last day of its daily record. On 2026-11-14 the table had about 8,900 gages, including canals, ditches and tidal streams. Updated daily.
- County drought categories. The weekly share of each county’s area in each Drought Monitor category: none, D0 abnormally dry, then D1 moderate through D4 exceptional drought. The categories don’t overlap and add up to 100. Each date is the map’s valid date, a Tuesday.
What the site adds: one schema and one place-ID scheme shared with its sister sites (usgs- plus the site number for gages, us-county- plus the FIPS code for counties, which the gage table also carries), files in JSON, CSV and Parquet, a version for every update, and checks before each one is published. If a check fails, the last good version stays live.
What it misses
Recent streamflow is provisional. USGS says provisional data are subject to revision and have not received final approval, so a recent value you download today may change. The provisional flag tells you which days. How far back it reaches varies by gage: for the Potomac gage tested below, it covered the last 38 days, from 2026-10-07.
Some days have no number. Discharge is null where USGS publishes a day without a value, for example because of ice, equipment problems or seasonal gages. Flow can be negative where tides or regulation push water upstream.
Only the last 400 days. Many gages have far longer daily records at USGS (the gage table lists record start dates back to 1861), but this site keeps only a rolling window, and only gages that reported in it. For long-term trends or a retired gage, go to USGS directly.
The Drought Monitor is a judgment, not a measurement. Its authors blend indicators such as rainfall, streamflow and soil moisture with impact reports and input from more than 450 local experts. The NDMC says it shows the big picture and advises against using it to infer specifics about local conditions. It looks back, not forward: the map uses data through Tuesday morning, comes out Thursday, and is not changed after it is published.
Area is not people. The county figures are shares of land area, so a county can be mostly in drought where few people live.
It’s a copy. For anything high-stakes, such as flood or water-supply decisions, use USGS and the Drought Monitor themselves.
How to access it
1Browse the datasets
Start at waterdata.dev/datasets/. Each dataset page shows its coverage, schema, license, credit line and every endpoint, with a chart.
2Find a gage
The gage table is split by state. https://api.waterdata.dev/v1/stream-gages/table/us-md.csv lists Maryland’s gages with their IDs, and /v1/stream-gages/table/all.csv returns every gage. Each dataset is also one CSV or Parquet file, at /v1/{dataset}/download/{dataset}.csv (or .parquet).
3Call the API
The base URL is https://api.waterdata.dev/v1. The catalog at /v1/catalog lists each dataset with its current version and coverage. Each series for each place is its own small file, at /v1/{dataset}/{series}/{location}.json (or .csv).
For example, https://api.waterdata.dev/v1/streamflow-daily/discharge/usgs-01646500.csv returns daily flow for the Potomac River near Washington, DC (Little Falls). Tested on 2026-11-14, it returned days from 2025-10-11 to 2026-11-13, with the latest days flagged provisional. https://api.waterdata.dev/v1/drought-county/area/us-county-06037.csv returned weekly drought shares for Los Angeles County from 2025-10-07 to 2026-11-10.
4Read the docs
The docs cover the URL scheme, place IDs, formats, versions, caching and errors. The API reference lists the exact URLs. Without a key you can make 120 requests a minute from one IP address, so download the bulk file for large pulls. The status page shows whether each dataset is current.
How to cite it
Cite the version you used, and credit the source with the exact text given on each dataset page and the sources page. For streamflow, that’s “Streamflow data courtesy of the U.S. Geological Survey.” The Drought Monitor’s terms require a longer credit naming the NDMC, USDA, NOAA and NASA.
Every update gets a version ID: the publish date plus the start of a hash, such as 2026-11-01.29270142b7. Put it after the dataset ID with @ to pin it, and a pinned URL always returns the same data. The site says to cite the monthly snapshots, the first version of each month, because those are kept permanently. Other versions may be removed after 30 days. /v1/{dataset}/versions lists them. Pinning matters more here than on most sites, because provisional streamflow changes and the window rolls forward.
A worked example, for the Potomac at Little Falls in the November 2026 snapshot:
Streamflow data courtesy of the U.S. Geological Survey, daily mean discharge, Potomac River near Wash, DC Little Falls Pump Sta (USGS 01646500). Retrieved via waterdata.dev, streamflow-daily version 2026-11-01.29270142b7, https://api.waterdata.dev/v1/streamflow-daily@2026-11-01.29270142b7/discharge/usgs-01646500.csv, accessed 14 November 2026. Recent values provisional.
Sources & further reading
End of page · Back to top