Every year your utility may send a report saying your water meets all federal standards. That's true — and it's also not the whole story. To understand why, you have to know how the limits are set.
Two different numbers
For each contaminant, the EPA sets two values. The first is the health goal (the MCLG) — the level below which there's no known health risk, based only on health. The second is the legal limit (the MCL) — which the law says must be set “as close to the health goal as feasible,” explicitly weighing cost and available treatment technology.
For many cancer-causing contaminants, the health goal is zero — but the legal limit is set higher because reaching zero isn't considered affordable. Water that meets the legal limit is legal. That is not the same as being without risk.
The gap between “legal” and “safe” isn't an accident. It's written into how the limits are built.
And the limits are old
Many federal limits haven't been updated in decades and don't reflect newer science. The legal limit for arsenic, for example, still carries a meaningful estimated lifetime cancer risk — far above the one-in-a-million risk level public-health scientists treat as protective. Nitrate's legal limit traces back to a 1962 concern about infants, not the cancer research that has emerged since.
How we read it instead
That's why we don't just check whether your water is legal. We compare each contaminant against a health-based standard — the level tied to a one-in-a-million lifetime cancer risk — drawn from California Public Health Goals, EPA health goals, and peer-reviewed studies. When something is many times above that level but still “legal,” we think you deserve to see it.
How to read your own report
- Look past “no violations.” That only means legal limits were met.
- Compare to health-based guidelines, not just the legal column.
- Focus on what's elevated for your household, and filter for those specifically.