Understanding Your Tap Water

Active Alerts

If you are experiencing a water, power, or sewer emergency or service problem call our 24-hour hotline at 3-1-1 or (415) 701-2311 from outside SF or log on at sf311.org. Learn more or review active service alerts .

Our tap water is among the best in the nation. We are proud of it and hope you are, too.

You might have specific questions about your tap water. We hope these subject specific fact sheets help answer those questions and direct you to further resources to find out even more.

How does the SFPUC check for contaminants?

Federal and state governments closely regulate drinking water. They limit how much of certain contaminants can exist in public water. Our laboratory is able to measure very small amounts of contaminants.

Contaminants can be measured in parts per million, parts per billion, or parts per trillion. That means one part of contaminant per volume of water. View our illustrations that compare parts per million, billion, and trillion to different measures of water.

Emerging Contaminant Monitoring

Unregulated microorganisms and synthetic or naturally-occurring chemicals that are not commonly monitored by water utilities are termed contaminants of emerging concern (CECs). More than 100,000 chemicals are registered in the US, and new chemicals and microorganisms continue to be identified. Some of these contaminants can be detected at extremely low levels in the environment by ever-improving laboratory methods. The health significance of these trace contaminants is typically unknown. We are proactively addressing CECs through participation in national research projects and conducting independent monitoring of our source and treated waters.

The 2025 CEC Progress Update Report will be provided upon request by emailing: quality@sfwater.org. To learn more, read the following fact sheets: