The market is the only mechanism that can allocate scarce resources equitably. The article is surprisingly good and mentions that the economic argument is not

The market is the only mechanism that can allocate scarce resources equitably. The article is surprisingly good and mentions that the economic argument is not so clear cut because the demand is inelastic. People still need to drink whatever the price. But if someone owns a resource, they have an interest in preserving it. There is also anecdotal evidence given in the article that this doesn't automatically happen. Privatised water utilities have cut down on staff and maintenance in order to maximise profit (since maximising profit is their reason for existing).