Can coronavirus contaminate public water systems?
Viruses can survive a few days in water, i.e. SARS can survive 22 days in lab grade reagent water and 7 days in pasteurized sewage. That is the time the virus takes to be at 99% of it's original concentration. (from "survival of surrogate coronavirus in water").

Viruses can also spread via swimming pools, i.e. hepatitus A and norovirus have been associated with swimming pools. (from "a review of waterborne viral deseases associated with swimming pools").

Boiling water will kill viruses. Children have very little reaction to the virus when they carry it, so it's likely that they act as a transmitter more than water does. I'm not worried about it at all by the way, just do what the doctors advise.