Great Forum! Lot's of info.

I am having a home built in the Bahamas and am starting to research how to sort out the water situation. It's a 1 bedroom, 1-1/2 bath (shower only, no tub) house that will be supplied entirely from a cistern. I am also considering a whole house RO Filtration system. I plan to use PEX in a home run configuration and will probably split it so that I feed the toilets, outside faucets, and possibly washing machine off of Non-RO purified water. Also the pump will be adjacent to the cistern and below the water level of it.

It seems that I would probably want to have separate pumps and tanks. Is my thinking right?

1)Cistern>Filter1>RO>Ambient Storage>Pump>Bladder Tank>CSV>Fixtures(Ro Filtered) ??
2)Cistern>Filter2>Pump2>Bladder Tank2>CSV2>Fixtures (non-RO Filtered) ??

I am considering limiting the water pressure to 40 PSI in an effort to conserve water(I'll probably rent this place). Could I go lower?

Also has anyone had any experience sizing cisterns. My architect designed for an 8K Gallon cistern, but I think I should have something closer to 20K. I realize that rain fall averages have much to do with this, but it gets pretty dry in the spring and summer months.

Finally I'm trying to understand exactly what a CSV is. It sounds like just a pressure regulator. Am I oversimplifying it, and if so what am I missing?