Well Lake Tahoe supplies the drinking water to much of Northern Nevada and Northern California. If the lead is improperly shielded or shielding has eroded then it's a pretty straightforward journey from there.
Lake Tahoe holds a truly massive amount of water. 37 trillion gallons of water. Mercury and arsenic contamination from all the abandon mines is a much bigger issue, and that isn't even a real risk to drinking water. (I get my water from the Truckee river)