How We Grade Water Quality

ClearWater grades are not issued by the EPA or any government agency. They are our own system for translating EPA compliance data into a simple A-F score.

Every public water system in the US is required to meet EPA standards and report violations to the Safe Drinking Water Information System (SDWIS). ClearWater pulls this data and computes a grade based on violations from the past 12 months, weighted by type and severity. Health-based violations carry the most weight because they indicate actual contamination or treatment failures that could affect your health.

We also factor in PFAS data from the EPA's UCMR5 monitoring program. If a water system has any PFAS compounds (PFOA, PFOS, PFHxS, PFNA, or GenX) detected above the EPA's Maximum Contaminant Levels, each over-limit compound counts as one recent health-based issue for grading purposes. This means PFAS contamination affects the grade the same way a recent violation would, even though formal SDWIS enforcement is still being phased in.

The grading criteria

Meets all standards

No health-based violations in the past year, no PFAS over the EPA limit, and 3 or fewer active violations of any type (including monitoring and reporting). This is the best possible score.

Generally safe

Exactly 1 health-based issue in the past year (a recent violation or one PFAS compound over the limit). The issue may have been brief or already resolved, but it's worth knowing about.

Some concern

2 to 4 health-based issues in the past year (violations plus any PFAS over the limit), or more than 3 active violations of any type. A pattern of issues that warrants attention.

Significant violations

5 or more health-based issues in the past year. This system has a serious pattern of recent compliance failures. Consider testing your tap water independently and using a filter.

Active health violation

At least one health-based violation is currently active (not yet resolved). This means the EPA considers the system out of compliance right now. Contact your utility and consider using bottled or filtered water until the issue is resolved.

What the grades don't tell you

An A grade means a system has met all EPA legal requirements. It does not mean the water is free of all contaminants. Many substances (like PFAS until recently) had no federal limit, and some health advocates argue that current EPA limits for certain contaminants are not strict enough. A system can have an A grade while still containing detectable levels of contaminants that are below the legal threshold.

Conversely, a low grade doesn't always mean the water is currently unsafe. A system might receive a C or D because of violations from the past year that have since been resolved. The grade reflects the last 12 months of compliance, not necessarily today's water quality.

These grades also only cover public water systems. If you're on a private well, there is no EPA oversight and no violation data to grade. See our well water testing guide for what to do instead.

Where the data comes from

All violation data comes from the EPA's Safe Drinking Water Information System (SDWIS). This is the same database that state regulators and the EPA use to track compliance. ClearWater queries this data through the EPA's public Envirofacts API and updates it quarterly.

A violation is classified as "health-based" if it involves a Maximum Contaminant Level (MCL) exceedance or a treatment technique failure. Monitoring and reporting violations (missed deadlines, late paperwork) are tracked separately and carry less weight in the grade.

A violation is considered "active" if it has not been marked as returned to compliance in the SDWIS database.

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