As far as water goes, it is no different than any other resource and as such is not immune from economic reality or truths. People care for that which they own, if no one owns it, you get the island of trash in the ocean. When you remove the incentive to care for th environment by collectivizing it you get exactly what would be expected by unowned property, it gets trashed.
Companies who benefit from selling products that purify water would help to keep it clean as well. If commercial drone traffic were legalized there could be trash drones that pick up trash. If a river ran through your prOperty and someone downstream polluted it and it affected you, you could sue them. Without private property there is no one to be angry and no one to sue.
Government is antithetical to environmental stewardship. The only way to safeguard the environment is by recognizing property rights, and the right to sue for damages. It is government that bombards the planet with nuclear and conventional weapons, operates the most fuel-inefficient vehicles, and protects corporations from liability for their actions. Governments also distort the market's natural rationing mechanisms through price controls, subsidies, and irrational regulations.
In contrast, a market with a manipulation-free price structure provides a distributed grassroots information network to signal supply and demand accurately, to better allow people to understand the availability of goods and services, and to provide automatic incentives for conservation or for exploration for new resources.