It is one of the few and necessary functions of government that it enforce property rights, and assist in codifying rational property rights when people come into conflict over what was the “commons”.
The West always had more conflicts over water, and developed an ad hoc property system that needs to be rationalized and fixed. It currently allocates more water than is available in low years and encourages wastage of water otherwise. We know a lot more about market systems now, and moving away from the semi-property right, semi-property of the commons system that we now have, to a full property right, market system is where we need to go to best allocate the use of the water.
The Colorado River Compact suffers from the allocations being based upon high precip years.
Water rights are not “semi property right” - they’re full property rights. That is true of water rights going back to before the southwest was part of the US. There are water rights on ranches in Nevada that exist prior to 1848 and are recognized in treaty.