Water Quality

MMWD takes many steps to ensure the water delivered to your tap is of high quality. These steps include responsibly managing our watershed lands and reservoirs, treating the water, operating and monitoring a complex distribution system, and maintaining and upgrading our facilities.

Information About Coronavirus (COVID-19)

With the recent news regarding coronavirus (COVID-19), we want you to know that this virus has no impact on the safety of your drinking water. Our water supply is locally sourced, with the majority of it coming from our protected Mt. Tam watershed. Your water is treated and routinely monitored to ensure there are no viruses or pathogens. We have plans in place to ensure that under any scenario, we will continue to provide you with safe, high-quality drinking water.


Every year, MMWD conducts more than 120,000 water quality and process control tests to ensure your water is safe to drink. MMWD looks for minerals, metals, salts and other similar chemicals. MMWD also tests for bacteria, herbicides, pesticides, endocrine disruptors, and industrial chemicals. In addition to the tests listed above, MMWD also tests your water to ensure the color and clarity are up to our high standards.

Tests are conducted from the time the water is collected in our reservoirs on the watershed, to the time the water arrives at your faucet. This includes testing in the lakes, at the inlet and outlet of the treatment plants, at key locations in the distribution system, and some at customers' taps. If you have any questions about your water quality, please contact our Water Quality Laboratory at 415-945-1550 or through email.

Public Health Goals

As a California water supplier, MMWD must prepare a special Public Health Goals Report every three years with information about contaminants that exceeded Public Health Goals (PHGs) or the U.S. EPA’s Maximum Contaminant Level Goals (MCLGs). PHGs are non-enforceable goals established by the CalEPA’s Office of Environmental Health Hazard Assessment and are not required to be met by any public water system. The U.S. EPA establishes MCLGs which, like PHGs, are non-enforceable goals.  

MMWD’s PHG report, which summarizes water quality data for 2016, 2017 and 2018, was presented at a District Operations Committee meeting on October 18, 2019. If you have any questions regarding this report, please contact the Water Quality Lab at (415) 945-1550 or email waterquality@marinwater.org.

Taste and Odor
Occasionally, some MMWD customers experience a different taste or odor in their drinking water. Some describe the water as tasting and smelling earthy, musty, or moldy. This is caused by naturally occurring compounds produced by algae blooms in our reservoirs. Algae blooms are a natural phenomenon in our reservoirs, particularly during the warm summer months, and are a reminder that our lakes are living water bodies.

Throughout the year, MMWD may shift water sources from one reservoir to another to accommodate maintenance projects. These operational changes can result in customers noticing changes to the taste and smell of their tap water.

Be assured that in spite of occasional variations in taste or odor, your water meets the highest standards for drinking water.