How to find out who supplies your drinking water

Start with the bill, the lease or the well

The quickest answer is usually on paper. If you pay for water, the utility that sends the bill is your supplier, or at least the retail end of it. If water is included in your rent or condo fees, ask the landlord, property manager or homeowners' association which utility serves the building.

If nobody sends a water bill and the property has its own well, you are probably on a private well, not a public water system. EPA says private domestic wells are not regulated under the Safe Drinking Water Act, and that the well owner is responsible for the safety of the water. EPA estimates that about 15% of Americans rely on private wells. None of the public-system records described below will cover a private well.

What counts as a public water system

Under federal rules, a public water system is one that provides water for human consumption through pipes or other constructed conveyances to at least 15 service connections, or that regularly serves an average of at least 25 people a day for at least 60 days a year. That covers far more than city utilities. EPA sorts these systems into three types:

• Community water systems serve at least 15 connections used by year-round residents, or regularly serve at least 25 year-round residents. Homes, apartments and mobile-home parks are served by these.
• Non-transient non-community systems regularly serve at least 25 of the same people for more than six months a year. EPA's examples are schools, factories, office buildings and hospitals that have their own water systems.
• Transient non-community systems serve places where people do not stay long; EPA's examples are gas stations and campgrounds.

AquaCensus lists 49,378 active community water systems, 17,037 non-transient non-community systems and 76,476 transient non-community systems. If you live in a home connected to a public supply, the system that serves it is a community water system.

The PWSID is the key to every record

Every public water system has a public water system identification number, or PWSID. EPA describes it as a two-letter state or region code followed by seven digits. Raleigh, North Carolina's city system, for example, is NC0392010.

The PWSID matters because system names repeat and change. There are many systems called something like "County Water District", and a utility can be renamed or merged. The PWSID stays with the system, and it is how EPA's compliance records, violation history and annual report tools tie back to one supplier. On AquaCensus, every system page shows the PWSID and uses it at the end of the page address.

Looking up your system on AquaCensus

AquaCensus organises EPA's inventory by place, so you can browse to your system without knowing its name:

1. Open Water systems and choose your state.
2. On the state page, choose your county. The county page lists its active systems, largest first, with population served and water source.
3. Open the system that matches your town or utility to see its type, owner type, source water, population served, the state agency that oversees it, and its recent violations.

A few things can make the match less obvious. Small towns are often served by a rural water district, water association or water supply corporation rather than a city department. A utility that spans several counties is listed on AquaCensus county pages under the first county it reported to EPA; its own page lists every county it serves, and the other counties' pages list it separately as also serving them. And a large utility may appear under the name of the city or authority that owns it rather than the name printed on your bill. If you are unsure between two candidates, your utility can confirm its PWSID.

When your utility buys its water from another one

The utility that bills you does not always treat the water. Federal rules call a system that receives some or all of its finished water from a wholesale system a consecutive system. In EPA's data this shows up as a "purchased" water source. Of the active community water systems in AquaCensus, 9,894 report purchased water as their primary source: 7,169 buy surface water, 2,615 buy groundwater and 110 buy groundwater under the influence of surface water.

For you, the retail utility is still the one to contact. When a wholesaler has a violation that requires public notice, the rules require it to notify the consecutive system, and the consecutive system is responsible for notifying the people it serves. The groundwater vs. surface water ranking shows how source water splits by state.

What to do once you know your system

Knowing your supplier opens up the records that answer the questions people usually have next:

• Water quality: community water systems must deliver an annual water quality report, called a Consumer Confidence Report, by July 1 each year. Your utility can send you a copy, and EPA keeps a search tool for reports that utilities have posted.
• Compliance history: the violations section of each AquaCensus system page lists the most recent Safe Drinking Water Act violations in EPA's records, with whether each one was health-based and its current status.
• Questions or concerns: the utility is the first call. Each AquaCensus system page also names the state drinking water program (the primacy agency) that oversees it, and EPA takes general drinking water questions through its online contact form.

AquaCensus is screening information drawn from public records, not a compliance determination or health advice. For the current status of your water, rely on your utility and your state drinking water program.