... and have for the last 10 years. You will pay anywhere from free (rare) to 60 cents a gallon for RO water. Some places you can pay $25 for all the water you want, like Valentine's Marina at Harbour Island, so when we're nearby, we stop for a morning, fill the tanks, give the boat a nice long wash in & out, wash the dinghy, flush the outboard, do some laundry at the dock, fill a few jerries, take a shower in the cockpit, wash the wetsuits.
If you are looking purely from a cost standpoint, I don't think a watermaker makes sense at all, you can buy a shitload of water at 60 cents before you break-even on the watermaker cost + annual filters, parts and so on.
We carry about 120 gallons of fresh water, we are three, we average about 10 gal/day for the three of us total, so we can easily go 10 days. We're in the water every day so we take showers every day, a quick rinse, I don't like salt down below. We're conservative but not overly so. We do not have a watermaker, however it is at the top of my list for reasons other than economy which you mention. I know nothing about the model you currently have and are considering parting ways with. I don't think I would, but I also don't know if it is a DC/AC, output, condition, maintenance, your boat, your sailing habits, etc.
If you've spent time in the Bahamas then you know water is available, sort of. If you are the social type and you like being places where lots of other boats and action are, then perhaps go without. We're not that way. We spend as little time as possible in popular places, we generally like being where there are few or no services, and no other boats, in the Out Islands. I have to carefully plan around where & when water will be available, and I don't like having to think about that every day, which I do. And I don't like being controlled by it. More than once we've had to leave a wonderful anchorage with great folks nearby we've just met to go get water, and weather in the Bahamas getting from like say Samana Cay to the nearest place that has water is an issue, and will take ALL day. And then you'd like to come back to Samana Cay, but the weather keeps you from doing that, when you could have stayed put, tucked in safe & sound in the first place. Our favorite places for cruising in the Bahamas are the southern islands ... Jumentos, Acklins, Crooked, the smaller islands around there, Conception, southern Eleuthera. You won't find water very easily in any of those places, certainly no where you can tie your boat and take on a bunch of liquid gold. When we're there, we'll get our average down to 5 gal/day, and then that's not a lot of fun. If you spend the winter in Georgetown, every week or so dinghy into Exuma Markets with your jerries and fill up for free. However, other than Emerald Bay, I don't know of any place in the southern Exumas, Georgetown included, where you can tie your boat up and take on water. I'd wash my boat with RO water from Exuma Docking but I wouldn't drink it. So make sure you have a strong back.
We once spent 3 weeks at Conception, the easterlies were honking 30 kts most the time, no way you'd want to leave and certainly not come back. It was us and a larger power boat we befriended, who gave us all the water we wanted. We had the place to ourselves, it was great, one of out most memorable times ever in the Bahamas. No way we could have done that, as comfortably as we did without water from that power boat. With a watermaker, you will become completely independent if that is what you want ... that is priceless. I guess what I am saying is, I personally would not look at this with some kind of financial break-even objective in mind.
I don't know what kind of boat you have. Ours is well loved, well taken care of and she looks great, lots of brightwork, we spend a lot of time in the cockpit and it generally is not very salty back there. It (usually) doesn't rain in the Bahamas, and it usually is quite windy. So, #1 you won't catch much if any rainwater; #2 if you do a fair bit of sailing and moving around in the open waters, your boat will be caked with salt, and I personally don't like that. She gets a fresh water wash as often as possible. With a water-maker, that could happen all the time ... at least the traffic areas, the Dodger, the glass, portlights & hatches. And #3, if I had a watermaker, I would plumb the Head with fresh water ... no smell, no gunk in the intake strainer that smells and should be cleaned every week or so, parts last longer.
There are plenty of days for whatever reason I can spend at least a half day getting water. Sometimes that's fun, sometimes you meet cute women hitchhiking back & forth with your water, sometimes it sucks ... getting there, playing tides, waiting on weather, waiting on the guy to come back from lunch, ferrying jerries back & forth, which gets really fun when its rough, or taking cabs from the quay to the source and back.
Now, if you spend a month on the boat, a month or two off, and do this on & off all year, then maybe the maintenance can get too much. But if you're on her for several months at a time, I'd keep it. One more thing ... if it is the Bahamas, then its the Bahamas ... you cannot trust the source of on-land RO water. I've had several times where we filled up from a reputable source only to find crap in my tanks, or fowl tasting water. There's only one thing that beats the taste of your own RO water from a well maintain & operating system, and that's rainwater, which is hard to come by in the Bahamas.
Hope this helps ...
Cheers, John