If you live in Philly and want to know information about your tap water quality, start with the latest consumer confidence report, which is required to be produced annually by every community water system in the country. Most people never read them, but the reports provide essential information about drinking water quality.

Like other large water systems, the Philadelphia Water Department publishes this information online, including the most recent 2025 drinking water quality report. The report provides an overview of Philly’s drinking water from source to tap. It reports that levels of approximately 100 regulated contaminants all meet federal standards.

As an interdisciplinary scientist and engineer, I study drinking water infrastructure and how science gets translated into policy and decision-making.

While the Philadelphia Water Department report is a good place to start, knowing what it tells you and where there may be gaps requires some background on how drinking water is regulated.

How drinking water gets regulated

In the U.S., drinking water is regulated under the Safe Drinking Water Act, which set limits for just over 20 contaminants when it became law in 1974.

Subsequent amendments and regulatory processes have brought the total to about 100. That’s still a small number compared to the approximately 700 disinfection byproducts, the tens of thousands of chemicals in commercial use in the U.S. today, or other contaminants of emerging concern.

While not all of these compounds end up in drinking water in amounts that can harm public health, the U.S. Environmental Protection Agency’s regulatory process is designed to be reactive, not proactive.

Before setting a limit, the EPA must demonstrate that a contaminant may cause adverse health effects, that it occurs at levels that are a public health concern, and that regulation would meaningfully reduce risk.

This process is repeated........

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