Water systems even if owned privately for profit are a regulated monopoly and behaves as a public utility (through regulation).

Certain systems are natural monopolies since it would be infeasible for multiple providers to set up and run the system. It would simply be too expensive for the consumer.

Capitalism isn't solely about consumer choice. It is related to the use of private capital for the provision of goods and services. There are many instances of cities collecting taxes and setting up municipal owned water systems (which is the complement of capitalism - the use of public capital raised through taxes).

Neither public nor private funding guarantees access, quality of services or low cost of services. So it would be a mistake to conflate one with the other. There is no free lunch - one way or the other someone has to pay for the service. Declaring something a "human right" is rhetorical because it says nothing for how such a "right" is to be provisioned or provided. (I can just as easily claim that everyone being a millionaire is a human right, but that doesn't make it happen without bad consequences)