Instantaneous Values service (IV)

IV is one of USGS Water Services' REST APIs for water observations, sitting beside the Daily Values and Statistics services. Its catalog record specifies the shape precisely:

• granularity: per-site, per-parameter readings at 5-60 minute intervals (IV)
• temporal coverage: Instantaneous Values retrievable from 2007-10-01 to present
• caveat: some unapproved data limited to 120 days

In practice that means each reading is keyed to a monitoring site and a measured parameter - streamflow and gage height being the headline pair - delivered at sub-hourly resolution across a network of gages, with the freshest values still subject to review.

Resolution is the whole point: IV is where sub-daily hydrology lives.

• Event-scale questions need IV. Flood peaks and rapid stage changes vanish in daily means; 5-60 minute readings catch them.
• The 120-day rule shapes pipelines. Unapproved recent data is limited to a 120-day window, so long-term archival of fresh readings must happen on your side.
• Provisional status travels with the numbers. Recent values carry USGS's provisional-data disclaimer - fine for monitoring, barred from legal or regulatory decisions until approved.
• Cost is not a barrier. USGS endpoints answer unauthenticated requests at no charge, one of the 1,437 free-of-charge entries among 1,744 cataloged datasets.

For day-level climatology instead, the companion Daily Values service is the better fit.

1. Confirm the interval matches your question. The service reports at 5-60 minute intervals; if your analysis needs only daily totals, DV or the Statistics endpoints are simpler.

1. Respect the 2007-10-01 start. Anything earlier needs a historical source - IV retrieval begins there, per the catalog record.

1. Separate approved from provisional. Readings inside the last 120 days may be unapproved; flag them in storage so the provisional disclaimer survives into your outputs.

1. Key on site and parameter together. Rows are per-site, per-parameter - build your schema around both keys or joins will duplicate.

1. Archive early. Unapproved recent data expires from the 120-day window, so schedule your own capture of fresh readings.

Services and caveats around USGS water data: - daily values service — USGS's summarized daily time series condensing each site-parameter to one value per day. - keyless public api — An API usable without registration, keys or payment. - provisional data disclaimer — USGS labels recent real-time readings provisional until reviewed, and the disclaimer bars their use in legal or regulatory decisions until approval. - streamflow gage height parameters — Streamflow and gage height are the headline measurements taken at USGS surface-water gages, returned per-site and per-parameter through the IV and DV services.