Short definition
Potable water is water safe for drinking, cooking, and food prep — meeting regulatory standards for chemical, microbiological, and physical quality. In the US, those standards come from the EPA’s Safe Drinking Water Act, with Washington state primacy administered by the Department of Health. If you’re on a public water system, what comes out of your tap is potable by definition; on a private well, you confirm it through testing.
What it is
A water sample is potable when it tests below maximum contaminant levels (MCLs) for the substances the EPA regulates: total coliform and E. coli for microbiological safety; lead, copper, arsenic, nitrates, and dozens of others for chemical safety; turbidity for physical quality. A regulated public water system samples and reports these continuously and publishes annual Consumer Confidence Reports. A private well doesn’t — testing is the homeowner’s responsibility.
The plumbing-system corollary is the lead-free standard. Since the 2011 EPA amendment, US-installed pipes, fittings, and fixtures used for potable water must be “lead-free”: not more than 0.25% lead averaged across the wetted surfaces, and not more than 0.2% in solder or flux. Older brass fittings and pre-1986 copper-with-lead-solder joints are why pre-1988 plumbing remains a household lead concern even after a utility has removed lead service lines.
Why it matters to a homeowner
If you’re on Seattle Public Utilities, Tacoma Water, Bellevue Utilities, Spokane Water Department, or any other Washington Group A system, your water arrives potable. The remaining lead and copper risk is your own household plumbing — older brass fittings, old copper joints with lead solder, and a small minority of homes with private-side lead service lines that the utility’s program hasn’t yet caught.
If you’re on a private well, “potable” is something you confirm through testing — annual coliform at minimum, with periodic testing for nitrates, arsenic (in Cascade-foothill areas), and any local concerns. A failed test usually traces to a failed well cap or surface water entry, not the aquifer itself.
When a real-estate transaction asks for a “potable water letter” on a well-served property, this is what they mean: a current passing water-quality test demonstrating the well meets drinking-water standards.
Washington note
Washington’s regulatory structure for potable water:
- Group A public systems (15+ connections or 25+ people for at least 60 days a year) are governed by WAC 246-290 under the Department of Health Office of Drinking Water.
- Group B systems (smaller community/shared installations) are governed by WAC 246-291.
- Single-family private wells are not regulated by DOH for ongoing testing; the homeowner is responsible.
- Lead and Copper Rule action level is 15 parts per billion for lead and 1.3 ppm for copper at the tap. Public utilities monitor and report; if a utility exceeds the action level, treatment changes follow.
- The 2011 lead-free amendment to the SDWA requires that any new pipe, fitting, or fixture installed for potable water service in the US be lead-free under the 0.25% / 0.2% standard.