If they did, they would be shut down, sued, tried for endangerment to society, and thrown in prison for a very long time. Intentionally polluting a water supply you are in charge of maintaining...
They cannot. The reason for companies charging for the water is due to the infrastructure and distribution. It takes a lot of money and resources to maintain the network of pipes, treatment plants,...
Water is purified at water treatment plants going under a series of different treatments: pH adjustment, Flocculation, Sedimentation, Filtration, and various disinfection processes.