Water Quality

The City of Napa is committed to providing a safe and reliable supply of drinking water that meets all State and Federal health standards. The Water Division’s three treatment plants transform raw source water into clean and safe drinking water using three basic steps - sedimentation, filtration, and disinfection. The water supply is continually sampled and tested for contaminants to ensure that health standards are met and that taste, odor, and appearance are optimized.


It's that time of year again...when Lake Hennessey is 'turning over.' Minerals and anaerobic materials from the bottom of the lake make their way through the water column to the top of the lake. This mineral and anaerobic material has greater taste and/or odor issues.

Cooler weather will increase algal-like odor in Lake Hennessey. Although algae is removed by our water treatment process, it can leave behind musty/earthy or metallic taste and/or odor. We constantly work to optimize the use of our available treatment capabilities at the Hennessey Treatment Plant, but must continue using water from all of out available sources to meet system demands.

To help alleviate any temporary adverse taste and/or odor, you can:

  • chill your tap water,
  • add citrus (lemons, limes, oranges, etc.) or cucumber,
  • aerate your water by swirling it in a large pitcher

Reporting a Problem with your Drinking Water

Before reporting a problem, please note whether your concern is with the water’s color, taste, odor, or something other, and be prepared to answer the following questions:

  • Is the problem in the hot water, cold water, or both?
  • Is the problem observed at all faucets?
  • Do neighbors see a similar problem?
  • Is there construction activity nearby?

Call Water Division staff at 707-257-9521.

View the City’s Monthly Summaries of Water Quality Complaints (PDF).

Annual Drinking Water Quality Report

Our drinking water routinely meets or exceeds the stringent water quality standards set by the U.S. Environmental Protection Agency (EPA) and the State Water Resources Control Board. As required by law, by July 1 each year the City provides its water customers with a summary of any contaminants detected for the previous calendar year.

Find out more about water quality reporting and view current and past issues of our annual Drinking Water Quality Report.