LOOK UP AS you enter Marin Municipal Water District’s Water Quality Laboratory and you’ll see where most of Marin County’s water comes from: Mount Tamalpais. On the day I visited, the peak was wrapped in a fluffy cloud muffler; the
autumn’s first storm had just deposited a much-needed con-
tribution to the seven reservoirs up there.
Three-quarters of our drinking water starts out as raindrops on Mount Tam, with the remaining quarter drawn from
deep below the Russian River, where it is naturally filtered by
60 feet of sand beds. Not everyone is lucky enough to drink
from such pristine sources. I, for instance, grew up drinking
from Lake Michigan, near Milwaukee, where in 1993 a protozoan called cryptosporidium sickened 400,000 people.
But just because the liquid in your tap flows from mountain
lakes and from far below ground doesn’t mean there’s nothing
but H2O in there. Inside MM WD’s Water Quality Lab, three
chemists work daily to measure just what is in your water, and
how much. They’re ready to take action if anything alarming
pops up in the samples continually taken from the reservoirs,
“Our lab probably does 2,000 to 2,500 analytical tests
per month,” says chemist Chris Nanney. “Forty years ago,
the primary function of a water quality lab was to do micro-
biology, to look at samples for total coliform and E. coli.
We still do a lot of that work,” Nanney says: in fact, on a lab
counter sits a tray full of plastic vessels the size of newborn
baby bottles, holding treated water that just tested negative
for those bacteria. “However, there has been a big emphasis
shift to chemical analysis,” he adds.
The lab is full of Rube Goldbergian machines, with fine
tubes winding around and through them and tall tanks of
helium and nitrogen standing by. One machine draws water
from amber glass vials the size of medicine bottles to make
sure the district’s two processing plants are filtering out
enough organic carbons — the product of decaying leaves, dead
fish and other yucky stuff found in nature. On another counter
hulks an ion chromatograph, used to analyze water samples
for fluoride, chloride, phosphate, sulfate and bromide.
What ’s IN
YOUR Water What exactly is coming out of our faucets — and how worried we should be about it. BY CARRIE KIRBY • ILLUSTRATIONS BY DAVE URBAN