If you want to see what US drinking water standards would look like if they were set by pure toxicology and cancer-risk modeling — with no compromises for regulatory feasibility or industry input — look at California.
California’s Public Health Goals (PHGs) are the strictest set of drinking water targets in the United States. They’re published by the Office of Environmental Health Hazard Assessment (OEHHA) at the California EPA, and they answer a specific question: at what concentration does this contaminant pose no significant health risk over a lifetime of exposure?
PHGs are not enforceable. They’re explicitly aspirational — the goal that California wants its drinking water to meet, even if state and federal legal limits permit higher levels. But because they’re calculated without the political and economic compromises baked into EPA’s federal limits, they reveal the gap between “what’s legal” and “what’s actually safe by current science.”
For TapWaterSafety, the California PHG is the strictest column in our utility-page comparison table. When a utility’s water exceeds the California PHG, it’s exceeding what California’s scientists consider protective — even if it’s legal everywhere in the US.
Why California has its own standards
The California Safe Drinking Water Act, passed in 1989 and amended periodically since, requires OEHHA to publish a Public Health Goal for every contaminant regulated by the state. The PHG must be set “at a level that, in the opinion of the Department, no known or anticipated adverse effects on the health of persons will occur, with an adequate margin of safety.”
That language matters. The federal Safe Drinking Water Act requires the EPA to balance health protection against the “cost” and “feasibility” of achieving the limit. California’s law has no such cost-benefit requirement at the PHG stage — OEHHA scientists set the value based purely on health protection, then California’s State Water Resources Control Board separately sets enforceable Maximum Contaminant Levels (MCLs) that consider cost and feasibility.
The result: California publishes both a PHG (the scientific target) and an MCL (the legal limit). Often there’s a substantial gap between them, and the PHG is roughly 10-1000x stricter than the EPA federal limit.
How PHGs compare to EPA limits
| Contaminant | EPA Federal Limit | California PHG | Difference |
|---|---|---|---|
| Lead | 15 ppb (action level) | 0.2 ppb | PHG is 75x stricter |
| Arsenic | 10 ppb | 0.004 ppb | PHG is 2,500x stricter |
| Chromium-6 | none | 0.02 ppb | EPA has no limit; PHG sets one |
| Vinyl chloride | 2 ppb | 0.05 ppb | PHG is 40x stricter |
| Benzene | 5 ppb | 0.15 ppb | PHG is 33x stricter |
| TCE | 5 ppb | 1.7 ppb | PHG is 3x stricter |
| PCE | 5 ppb | 0.06 ppb | PHG is 83x stricter |
| Mercury | 2 ppb | 1.2 ppb | PHG slightly stricter |
| Atrazine | 3 ppb | 0.15 ppb | PHG is 20x stricter |
| Trichloroethylene | 5 ppb | 1.7 ppb | PHG is 3x stricter |
| 1,4-Dioxane | none federally | 1 ppb | EPA has no limit |
| Radon | none federally | 100 pCi/L | EPA has no limit |
| Beryllium | 4 ppb | 1 ppb | PHG is 4x stricter |
The pattern is consistent: California’s scientific assessment of safe drinking water is 5x to 2,500x stricter than the EPA’s federal limits for the contaminants where there’s a documented gap.
How PHGs are calculated
OEHHA’s PHG methodology is published openly. For non-carcinogens, the calculation looks roughly like this:
- Identify the most sensitive endpoint — the health effect that occurs at the lowest dose
- Determine the No-Observed-Adverse-Effect-Level (NOAEL) from animal or human studies
- Apply uncertainty factors of 10x each for: interspecies variation, intraspecies variation, subchronic-to-chronic extrapolation, and database adequacy (typically 1000-3000x total)
- Calculate Acceptable Daily Intake (ADI) for a 70kg adult
- Set the source allocation — typically 20% of total exposure should come from drinking water
- Calculate the PHG in ppb
For carcinogens, the calculation targets a lifetime cancer risk of one in one million (10⁻⁶), compared to EPA’s typical target of one in 10,000 (10⁻⁴). That alone explains a 100x stricter PHG for many carcinogens.
The arsenic PHG of 0.004 ppb illustrates the methodology dramatically. Arsenic is a Group 1 carcinogen. At the EPA’s 10 ppb legal limit, lifetime cancer risk modeling suggests roughly 1 in 1,000 to 1 in 10,000 excess cancer cases per million people exposed. California’s PHG of 0.004 ppb is the level at which that risk drops to 1 in 1 million — California’s regulatory target risk. The EPA accepts 1,000-10,000x more cancer risk than California aspires to.
Why doesn’t California enforce its PHGs?
The PHGs are aspirational because achieving them is technically infeasible with current treatment technology and economically impossible for most utilities. A water utility that genuinely had to reduce lead to 0.2 ppb would need to replace every lead service line in its system, ban all brass fixtures in customer plumbing, and likely use reverse osmosis as a primary treatment step. The cost would run into hundreds of billions of dollars nationally.
California has separate state MCLs that are typically stricter than EPA federal limits but more achievable than PHGs. For lead, California’s state MCL aligns with the EPA’s 15 ppb action level. For arsenic, California’s MCL is 10 ppb (matching EPA). For TCE, California’s MCL is 5 ppb (matching EPA).
The PHG functions as a target rather than a rule. Utilities track progress against it. New treatment investments are evaluated against how close they get water to the PHG. And when treatment upgrades happen anyway (for other reasons), utilities preferentially install technology that moves them toward PHGs rather than just meeting MCLs.
Why PHGs matter even outside California
California’s PHGs are widely cited by:
- Federal regulators when proposing new EPA rules. The EPA’s 2024 PFAS rule was informed by California’s earlier state-level PFAS Public Health Goals.
- Other states. Massachusetts, New Jersey, New York, and Washington have all adopted contaminant limits stricter than EPA federal limits, citing California PHGs as the scientific basis.
- Plaintiff attorneys. In water contamination lawsuits, California PHGs are routinely cited as evidence of what reasonable scientific consensus considers safe.
- Environmental health researchers. Peer-reviewed papers on US drinking water risk use California PHGs as the benchmark for “safe” rather than EPA legal limits.
For a US homeowner asking “is my tap water safe?” — the most honest answer is: it’s safe by US federal law, possibly not safe by California’s scientific standard.
On TapWaterSafety pages
Every contaminant on every utility page shows the California PHG column alongside EPA, EU DWD, WHO, and EWG values. When detected levels exceed the PHG, the comparison is visible — but we don’t flag PHG exceedances as “violations” the way we do for EPA. The PHG is a goal, not a rule.
The reason we show it: knowing the strictest target makes the EPA limit feel less reassuring. A utility delivering water at 8 ppb arsenic is fully EPA-compliant and is delivering water 2,000x worse than what California aspires to.
That gap is the basic premise of TapWaterSafety. Federal compliance is not the same as health protection. The California PHG is the strictest available evidence-based benchmark for what health protection actually requires.
What you can do
If your TapWaterSafety utility page shows contaminants exceeding the California PHG — and it almost certainly does, for arsenic, lead, chromium-6, or trichloroethylene if any are detected — the practical response is the same one we recommend for any concerning contaminant: a properly certified home filter at the kitchen tap.
For lead and arsenic: NSF/ANSI 53 certified filter (typical pitcher or under-sink) or reverse osmosis (NSF/ANSI 58).
For chromium-6: reverse osmosis specifically. Standard carbon filters won’t reduce Cr-6.
For volatile organic compounds (vinyl chloride, TCE, PCE, benzene): activated carbon block (NSF/ANSI 53) at minimum, RO ideally.
These technologies aren’t expensive — most quality systems are $80-$700. The mismatch is that they shift the burden from utility to consumer, which is the wrong incentive structure but the only practical near-term solution.
Find your specific utility’s data, including the California PHG comparison, on its TapWaterSafety page.