RO plants are expensive to build, expensive to run, and subject to both regular, and unplanned, maintenance and overhaul. If the flush and de-mineralization cycles are not kept up, or if the intake sucks up oil, the membranes can be destroyed long before their expected life-cycle.

South Florida has played with RO plants. They even built a few small ones as proof-of-concept. The military has used small ones for years.

Every time water gets to be a major issue in south Florida two plans pop up. RO plants, and a pipeline to shift the "excess" fresh water from central and north Florida down south. Costs (Big $) and political pressures (What do you mean Miami has the right to drain central Florida lakes to keep their golf courses around Miami wet?) delay the issue until a hurricane comes along and kicks the can down the road a few years. Wash, rinse, repeat.

An interesting shift can sometimes to be seen in some people who have previously loudly objected to legal mandates for low-flow shower heads and low water use toilets. Their interests now clearly counter their previous highly principled views they now enthusiastically support what they had condemned. Sails are trimmed and most people, yours truly excepted, are too polite to take notice publicly.