You don’t have to tour this lab to find out what’s in Marin’s
water and what’s not; the lab puts out an annual report to tell
you. Still, here are some of those findings and what you should
know about them:
What’s in Your Tap Water
If you fill a one-liter pitcher with tap water in any of the 10
towns and cities or unincorporated areas MMWD serves,
it will contain up to 2.5 mg of chloramine, a combination of
chlorine and ammonia used to kill viruses and bacteria, such
as E. coli. MM WD uses chloramine in addition to chlorine
because it lasts longer, an important quality for a water system
that is spread out across a greater distance and a wider range
of elevations than many systems.
This residual disinfectant is the reason that some people
detect a chlorine taste in their tap water; you can remove that
taste by using a filter or by letting water sit in the fridge for a
while to allow the offending compound to dissipate. Although
the Environmental Protection Agency deems chloramine safe
for drinking water at levels more than twice the amount found
in Marin’s water, some people oppose the use of this disinfectant at any level, such as the Bay Area group Citizens Concerned
About Chloramine, whose members believe chloramine can
cause health problems like asthma or skin disorders.
• Haloacetic Acids and Trihalomethanes
That liter of tap water will also contain up to a few dozen
These compounds are the result of disinfectants — chlo-
micrograms of these chemicals, which, if consumed above
recommended levels for many years, are associated with
increased risk of cancer and other health problems. However,
Marin Municipal Water District’s product comes in at an aver-
age of half the maximum level regulators deem safe.
rine and chloramines — reacting with organic carbons. The
reason MMWD filters out 25 to 35 percent of total organic
carbons is to keep these byproducts low.
Reviewing MMWD’s 2015 water report, Natural
Resources Defense Council senior attorney Mae Wu saw no
cause for alarm in Marin’s levels of disinfectants or disinfectant byproducts. “While there may be some potential health
concerns with them, it’s nothing compared to everybody
dying of dysentery,” she says.
Every time San Rafael resident Mary Larkin turns on her
kitchen tap to get a drink of water, the liquid flows through a
two-tower reverse-osmosis filter sitting on her countertop.
Then she squeezes an eyedropper full of supplements into
the water to put back some of the healthy minerals this filter
removes. Larkin goes through this cumbersome and expensive process because she believes that the fluoride in Marin’s
water is hazardous to her family’s health.
She’s not alone. Of all the ingredients in Marin water, the
added fluoride — . 7 mg per liter, recently decreased from . 9 mg
due to a regulatory change — is the most controversial. In fact,
local group Clean Water Sonoma-Marin is collecting signatures for a proposed 2016 ballot measure to put a moratorium
on fluoridation. Marin residents voted in 1972 and 1978 to
fluoridate the water, and a 1995 California law requires it for
Inside MMWD’s Water Quality Lab, three chemists work daily
to measure just what is in your water, and how much.