1. Something that can't be taken away by someone else.
2. A contract between an individual and the country/state with which they are a citizen. In return for paying taxes and following laws, they can expect services, utilities, military, education, etc.
3. These things are not something you're entitled to morally (like water, as there's no one to sue if you don't have water in your region), but societies should recognize the need for water, and thus it is moral and right to help ensure that all people have access.