Water is not a right. Physical objects are not rights. If you own the water, then you have a right to act to protect it from theft or pollution.
Because you need an object to survive does not mean you have a right to the object.
You have a right to self preservation. That does not mean you have a right to a gun, ie a right for someone else to buy you a gun.
By the same right of self preservation you have a right to arrange to trade goods or services in exchange for healthcare services. You even have a right to do so if the law says that the person may not provide those services unless the person has permission, ie a license, to do so.
You do not have a right to force that person to provide that service, nor do you have a right to force another to pay the provider.
Obviously you do not have a right to air either. Now the matter of where and when air becomes property is interesting but another lesson, but the short version is it costs more to assert property rights than one gains by doing so, so it's not property. When water is superabundant no one cares. When it's in short supply the cost to maintain property rights is lower than the cost not to do so, and water becomes property.
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