There are illegal marijuana gardens in them thar hills -- which means there could be toxins in that thar drinking water.
Police routinely pull rogue marijuana gardens out of the woods above Crystal Springs Reservoir, which provides drinking water for San Francisco and for northern San Mateo County, according to the Bay Area News Group.
They pull plants, and they've also pulled "7,200 pounds of trash" last week alone, the newspaper reported -- and some of that trash includes "car batteries" and "toxic pesticides that have been banned in the United States."
As of yet, no "evidence the toxins have harmed the safety of the water" has been unearthed in any of the "100,000 tests" conducted per year, the newspaper reported.
In the most recent raid on Aug. 27, authorities grabbed 1,579 plants -- and also discovered "propane tanks, fertilizer, household garbage" and a pesticide called "Weevil-Cide," the newspaper reported.
No one was arrested, according to the newspaper.
Officials with the San Francisco Public Utilities Commission, which monitors the water's safety, said that no trace of the pesticides have been found in the reservoir.