How this is built
Methodology
What data The Waterline pulls, where it comes from, and how often it refreshes.
What we pull, and from where
Six sources, all public agencies:
- Reservoir storage comes from the US Bureau of Reclamation's RISE API: daily storage readings in acre-feet for every reservoir on the site.
- Streamflow comes from the USGS Water Data API: daily flows in cubic feet per second for every gauge on the site.
- California state reservoirs come from the California Data Exchange Center (CDEC): daily storage for the big state-run reservoirs the RISE feed does not carry, Oroville and New Don Pedro.
- Snowpack comes from the NRCS SNOTEL network: snow-water-equivalent readings across the West. Snow accumulates October through April and melts out by early summer, so these series sit near zero June through September by nature.
- Drought class comes from the US Drought Monitor, which publishes one national map each Thursday morning.
- CVP and SWP allocation percentages are read out of the operating agencies' own press releases as they are announced. Allocations follow no schedule: a handful of announcements land each year, mostly winter through late spring, and each update on the site is dated to its announcement.
How often
The pull runs weekly, each Thursday after the Drought Monitor's morning release, so the new drought map and the week's reservoir and gauge readings land together. Each pull covers a trailing two-week window, not just the newest day, so a missed week backfills on the next run. Every data page carries two dates: "data through" is the newest reading in the data itself, and "page updated" is when the page was last rebuilt.
For how to read the numbers once they are in front of you, see how to read this.
Republishing our charts and statistics
The charts and statistics on The Waterline are free to republish. Use them in an article, a report, a class, a presentation, or a post — you do not need to ask us first. We ask one thing in return: credit The Waterline with a visible link back to the page you took the figure or chart from, and keep that link live.
Every chart has an Embed chart button with a snippet you can paste straight into a web page. Because it points at the live image, the chart you embed today keeps updating itself as new data lands — you never have to swap in a fresh screenshot. Every data page, guide, and issue has a Cite button that hands you a ready-made citation line, including the date the data runs through. If you are quoting a number, keep that date: it is what tells your reader how current the figure is.