One way we do that is by banding together with our neighbors to form cities or other municipalities that tax us and use the proceeds to build safe water systems. If we elect untrustworthy or incompetent people to run those water systems then we have no one to blame but ourselves. If a city doesn’t have a law requiring the administrators of the water system to speak truthfully to the public then that is the people’s fault, not the government’s fault.
Honestly though I bet we’ll find that the administrators have technically been telling the truth. We have federal standards for things like water safety that are used to regulate water providers (which are not always public entities, mind you). Those standards do tell us how much lead in the water is acceptable and how much is unsafe, but those are two different numbers. The acceptable level is well below the threshold of safety. When this eventually gets to a trial in front of a jury I bet the administrators will argue that they were perfectly correct; that the water was safe because the levels of contaminates, although elevated, were below harmful levels.
The plaintiffs also complain about repeated boil–water notices, but that may not help their case. Any time you dig up a water pipe to repair or replace it then people using that water will need to boil it. Those notices are themselves proof that the utility was doing maintenance and repair work (presumably with the goal of fixing the problem), not proof of incompetence.
I’m not sure I’d want to be on that jury.