[copycat]

Would e coli, introuduced to a water supply, multiply until it reached toxic levels?

[Poohbah]

Considering how much chlorine gets put into municipal water supplies, I'd sooner worry about chlorine poisoning than E. Coli from the water supply.

[Untouchable]

High concentrations of E-Coli are found in fecal materials. If there were enough fecal material introduced to the water supply (and the conditions were favorable), the E-Coli would survive. Many agencies test water for E-Coli already.

[jae471]

E coli is not necessarily bad. It makes up a good portion of the bacteria in your intestines right now. It is harmless, except for one particular strain, O157:H7. O157:H7 produces a toxin that causes internal hemorrhaging and diarrhea.

Dumping e coli into water supplies may even be beneficial, since e coli produces vitamin k and b-complex vitamins.

Getting e coli is easy, scoop up some feces. Getting O157:H7 requires alot more work. I would be more worried about someone dropping a dead european cow into the water.