This is a curious way to put it. No matter what legal rights to water we have previously allocated, when everybody is going to be short of water - the legal rights only go so far. The whole reason for society to invest in carbon emission reductions, was to avoid difficult and costly outcomes like this.
The most legal solution to the legal shortfalls would likely for the right holders to go sue fossil fuel companies.
If someone neglects to clear their home area of burn material, and their house catches fire then burns their neighbors house - there certainly is a liability.
We live in a society where individual actions and rights have boundaries when they cause social effects. Part of goverments function is working out the fair way to discuss and act one it - particularly during trying times - like mass regional drought.
> If someone neglects to clear their home area of burn material, and their house catches fire then burns their neighbors house - there certainly is a liability.
This is actually incorrect. Liability only exists if you start the fire (and often times requires the element of negligence or intent).
> We live in a society where individual actions and rights have boundaries when they cause social effects
And that's why it's illegal to siphon your neighbors groundwater. We have hundreds of years of court cases on groundwater rights and they are generally clear - the owner of the land has rights to the groundwater before appropriation.
You can't build your home in a desert and then complain that it's a desert. That's a you problem. Go live somewhere with water.
The most legal solution to the legal shortfalls would likely for the right holders to go sue fossil fuel companies.