All rights are government-guaranteed. Who else? Your right to not be stabbed is enforced by the latent threat of prison and the police. Why would it matter if the right comes in form of an action (or prevention of one) or a physical good?
Because one of those things is materially rivalrous and it's important to acknowledge that. There is an explicit choice to distribute it politically, whereas something like police protection is inherently and unambiguously political.
Fwiw I don't think there's an inherent right to property.
Also the important thing is (presumably) you don't care who provides the water, just that humans get the water. Suppose fresh water were not the responsibility of governments, but NGOs, and everyone were provided water. Would you still consider it necessary "right"? Before you say "governments are more stable" I don't think there is any reason to believe that a government is more capable of equitably redistributing water to people in need; you money going to water is also wrapped up in money that goes to bomb people with different skin color halfway around the world, or XYZ things you don't care for your government to do; a nonprofit is typically slightly more focused in its mission and more effective at delivering that need, at least on a cost basis.
It's hard to make that argument with police forces; private police forces would probably be a terrible idea.