They don't if they have their own wells. Did you know that the system of dams and canals that deliver water to farms were built by the state and federal government to promote farming where natural conditions would make farming difficult?
Water rights are a big issue in areas where natural rainfall does not occur at the right time to support farming. Perhaps you think each farmer should work it out for himself? If each farmer worked it out for himself, then perhaps fewer farms would exist. That would be the free market too.
Why don't Americans demand a truly level playing field in trade, instead of allowing the third world to have the competitive advantage through trade agreements?
You don't want a level playing field, you want one that constructed to your advantage. There is no free lunch. You like the government handouts and rail against the rules that come with it.