While it's true watermakers are expensive they allow you freedom to cruise to remote areas that otherwise will be inaccessible. We use about 6 gallons a day. I don't know how but that's what it worked out to be. That will mean lugging a 5 gallon gerry can daily which is a little over 40lbs. Water is not always available in places for example the remote anchorages in the Bahamas which is anywhere other than communities which have marinas.
For some reason watermakers are advertised in gallons per day. I have found that to be deceptive. Who needs 200 gallons per day? In my opinion the way to look at it is how much water do I need per day and how long are you willing to spend making it. The with the Katadyn 40, the 40 gallon per day sounds like lots but it will take 4 hours to make that 6 gallons. I have the 80 but if I had known what I know now I would have bought the 160.
Another major consideration is electrical power. Battery capacity - daily amp hour consumption - and means of charging -solar, wind and mechanical.
Food storage. Refrigeration/freezer. We have a small built-in refer but carry an Engel 45 which we use as a freezer. This allows us to be away from stores for weeks at a time and we eat very well.
Dinghy, this is the family car when cruising so you need a good one with a decent size motor. Sometimes it's necessary to go a fair distance or the currents are strong.
A full cockpit enclosure. about 90% or more of your time is spent not moving and the extra space is well worth it. Also when underway and its raining it can be pretty unpleasant without shelter.
I agree, the first watermaker I bought was too small for long range cruising, it took too much time and too much current over that time to do what I wanted it to do. The second one I bought was a unit rated at 200 gallons per day, and did well. I put in two solar panels, the windcharger system, and rarely had to run the engines to charge the house batteries, when I did I made water, charged batteries, made radio transmissions, and did my housekeeping with the vacuum while the engine was running. I installed a 175 amp alternator to handle the load, and it did just what I designed the system to do, and did it without a strain.
Cruising in blue water and island hopping in the Caribbean, or coasting South America, Africa, or even the Med would, to me, not be easy without the water on board to be able to do it comfortably. I used a little over 30 gallons a day with three to four persons aboard the last time I went for an extended cruise. I have been looking at the energy efficient systems, like Spectra and some others, and I am very impressed with them. The key seems to be getting good pre-filtration, and using the fresh water flush on a schedule so you preserve the membrane, and keep little dead sea critters from clogging it up or ruining it, the membrane traps the micro organisms, and you get clean water, but you need to flush them with fresh water to keep their little dead bodies from mucking up the system.
Just like every other system on board I have redundancy planned. I have one of the manual, hand pumped water makers, it can make about 2 gallons in an hour of pumping the silly thing. I have it just in case of an emergency, I hope I never have to use it, but it is in an abandon ship bag with some other stuff I never want to use like the EPIRB. If you have a dinghy, or life raft, you need an abandon ship bag ready to go, sealed, water tight, and light weight to throw in it in the horrible case of your vessel capsizing at sea. It just could be that this would save your life and the lives of the members of your crew. How many cruisers have lost their boat and suffered horribly in a life raft, well I do not know, but I do not want to join them. If I should lose my vessel, I certainly want to know that I am prepared and can make it for more than three days in the life raft. If I go overboard without the EPIRB, the bag, or the raft...well I am going to be screwed if I am alone, but that is why we always do our best to practice safety, especially when we are alone. Prepare for the worst and pray it never happens.
I know I spend a lot of money on things that others say are not totally necessary. I also know I am not like many others, when I get back on the water this time I will be living on my boat for a minimum of two to five years, no house, no car, and no bills for electricity, water, and sewer, but if I lived on land I would spend over $2000.00 a year on just household water, not bottled water, the tap water. Where I live my water bill, not including the trash and sewer is routinely over $200.00 and goes as high as $300.00 per month. Maybe this is why I plan to spend the up front for a well thought out and well designed water maker system, because I know water is not cheap in most places.
If you have sailed the BVI, Bahamas, and Atlantic coast of South America you know that away from the crowds it is hard to find good, clean water for your tanks, and you are oh so right about those heavy jerry cans. It is bad enough having to lug ten of the five gallon diesel cans back to the boat in the dinghy, heft them over the rail, and lash them down, after making the first trip to fill the tanks. Ask any long range cruiser, read their blogs, ask them how much fun those cans are to wrestle with in a choppy anchorage. Yes, when you are sailing in the Chesapeake Bay, or the Great Lakes, or even cruising coastal Florida, or the Gulf of Mexico and never more than 10 hours from a great US marina then the watermaker sounds very unnecessary, when you are making for Tahiti from Colon Panama, well it might be more desired. Catching water from your sails sounds workable, but if it does not rain it is going to suck to be you.