How do I find out where my tap water comes from?

Enter your address on wherewaters.com. It finds the public water system that serves you from EPA's service area map, then shows that system's rivers, reservoirs, aquifers and treatment plants, plus live levels where gauges exist.

Where does your tap water come from?

Q: What if no water system shows up for my address?

Homes outside a mapped utility service area usually use a private well. wherewaters then shows the nearest USGS groundwater wells and how their water levels compare with a year ago.

Q: Is my tap water safe?

wherewaters shows your system's EPA violations from the last ten years and its recent lead test results. Your utility's annual water quality report, the Consumer Confidence Report, is the official source and is linked when one can be found.

wherewaters follows the water in your tap backwards: from your faucet to the treatment plant, to the river, reservoir or aquifer it was drawn from, up to the rain and snow that filled it. Enter any US address to see it on a map, with live levels.

What you see for an address

Your water system. The public water system whose service area covers the address, how many people it serves, and whether it buys its water wholesale from a bigger utility.
Its sources. Each river intake, reservoir, lake and well field, with what fills it: snowmelt from a named mountain range, rain over a basin, or recharge into an aquifer. Water bought from another utility is traced to that utility's sources.
The watershed. The land that drains to each surface source and the rivers flowing into it, drawn from the USGS national river network.
Live levels. How full reservoirs are against their capacity and a year ago, river flow at the nearest stream gauges compared with normal for the date, snowpack in the watershed compared with the median, and groundwater depth at nearby monitoring wells.
Treatment and safety. Treatment plants, the disinfectant used, fluoride and hardness, EPA violations from the last ten years, and the latest lead test results.
After the drain. Where your wastewater is cleaned and which river or bay it goes back to.

How it works

Every community water system in the US has an ID in EPA's Safe Drinking Water Information System (SDWIS). EPA also publishes a national map of those systems' service areas. wherewaters looks up the area containing your address, then reads the system's federal record: its intakes, wells, treatment plants, the systems it buys from, its violations and its lead and copper results.

The federal record names sources but doesn't map them, for security reasons. So the first time anyone looks up a system, Claude (an AI model from Anthropic) reads that record and searches the utility's own pages and annual water quality report to write a short profile: where the water comes from, what feeds each source, roughly where it is, and how it's treated. That takes about a minute and is saved, so the next person gets it right away. Profiles are refreshed every few months.

Live data comes straight from the agencies that measure it, cached for under an hour.

Reading the river gauges

Each gauge compares the latest flow with the same calendar day in all past years at that gauge, the way the USGS WaterWatch maps do:

Label	Means today's flow is
Much below normal	lower than 90% of past years on this date
Below normal	in the lowest quarter of past years
Normal	in the middle half
Above normal	in the highest quarter
Much above normal	higher than 90% of past years

Flow is in cubic feet per second (cfs): one cfs is about 450 gallons a minute. Reservoir storage is in acre-feet: enough water to cover an acre one foot deep, about 326,000 gallons, or roughly what two to three typical households use in a year.

Data sources

Water systems, violations, lead	EPA SDWIS via Envirofacts
Service areas	EPA Community Water System Service Area Boundaries
Rivers and watersheds	USGS Network Linked Data Index (NHDPlus)
River flow, reservoirs, wells	USGS Water Data; California Data Exchange Center (CDEC); Colorado Division of Water Resources
Snowpack	NRCS SNOTEL
Drought	US Drought Monitor
Addresses	US Census Geocoder, OpenStreetMap Nominatim
Map	OpenFreeMap, OpenStreetMap contributors

Questions

What if no water system shows up for my address?

EPA's map covers community water systems, which serve about 9 in 10 Americans. Outside them, homes usually have a private well. wherewaters then shows the nearest USGS groundwater wells and how their levels compare with a year ago. Private wells aren't regulated by EPA, so testing is up to the owner.

Is my tap water safe?

wherewaters shows the federal record, which is a good first look: health-based violations are the ones that matter most, while monitoring and reporting violations mean paperwork or a missed test. Lead mostly comes from old service lines and home plumbing rather than the source, so results vary house to house. Your utility's annual Consumer Confidence Report is the official word.

Can the research be wrong?

Yes. Claude only uses what it finds, links the pages it read, and leaves out what it can't confirm, but utilities change sources and AI can misread a page. Every profile says when it was written and links to its sources.

Why do the levels say "No live gauges report on this source"?

Many small reservoirs and most wells aren't on a real-time feed. Federal and large state reservoirs, and most rivers big enough to supply a city, are.