the easiest and cheapest way to have a watermaker
is to buid one yourself (assuming you are fairly handy and want it simple). grainger carries most of what you need as far as pumps etc, then the internet
will set you up w/ filter housings/filters, membrane housings/membranes and the rest is easy (relatively speaking). i was going to do it 15 yrs ago but when i totaled up the cost i found out about SK Watermakers in ft pierce (now vero bch, fl) and their price
for what i wanted (no frills just 15-20 gal/hr) was only $200 more than if i was to build it and i figured my time and the warranty was worth the extra $$$...i'm sure nowadays one can find instructions online on how to DIY...