The first thing you should have is good, working EPIRB; and the second thing you should have is a good real life raft which is inspected and ready to go; and the third thing you have is another EPIRB.

If you have a boni-fide raft, then you have water avaialbe for several days by mandate. In that case you already have enough water to expect rescue within the "normal" frame of reference if i) your EPIRB works; and ii) you're not in the middle of some obscure, out of the way, inaccessible rescue location. [Jerry, you're not going into such a place anytime soon.] If you have a raft, you won't have room for anything more than either i) a small PUR (not the 35); or, ii) another EPIRB. Buy the EPIRB, it's more likely to save you.

If you subscribe to the armagedon situation (where rescue isn't coming) -- take the PUR 35 and put in a ditch bag.

If you are going to be making some ocean passages, don't have twice the water you would need, and don't want to call out the cavalry to help -- then get a PUR 35, put it in the ditch bag, and use it in case you have to generate water to allow you get to where you are going without having the yell fo help.

Don't commission the the PUR 35 -- leave it dry and clean; or be prepared to cycle it every 3 or 4 months, then preserve the membranes. Once you commission it, I belive you have to keep cycling and protecting it periodically "forever".

We have a perfectly wonderful water maker that really hasn't been required by out cruising. It's a great unit, but it requres periodic maintenance and is a pain to put anti-freeze in over the winter (You can't dry it out, or through-away the membranes). If you're cruising to out-of-the-way places or over distances where you can't deal with the tankage, then they're great -- but otherwise, they're part of the dream we all have of doing that, rather than a practical necessity.