One of the things we want to add in the coming year is a watermaker. We researched them a few years back and were leaning toward a Spectra (http://www.spectrawatermakers.com/), but we saw lots of new models at the Southampton Boat Show. Now we are confused again. We would appreciate any advice, pro or con, about watermakers with which you have personal experience. Others to consider - any to stay away from.

Vice Commodore, OCC 

I love watermakers. The freedom they provide and the comfort of knowing where your water comes from is great.
I built our watermaker from Ebay parts. The total cost was £1500. We make 130 litres/hour in the Caribbean warm waters. Having had a12v system on our last boat i didn 't want to go that route again.
The current watermaker runs off the generator although if we didn 't have a generator i would have gone engine driven. Our watermaker consists of a 1.5kw 220v motor and a cat 247 pump. We currently use a 40" and a 21" membrane. The system has no electronics and the only electrics are the power supply to the motor. The system is super simple and we love it like that. This summer we plan to add a second 40" membrane that should take our output close to 200 litres/ hour for no more power consumption.
The reason we went for this set up is the inherent problems with 12v installations. To achieve reasonable output from the watermaker, say 50-70 litres per hour you are likely to be pulling serious amps at 12v even with the energy recovery pumps that are typically installed on these systems. It is not unusually to see 40amps at 12v. The size of cables at this kind of current is getting pretty meaty. You need to use tinned wire as the risk of high resistance in plain copper is a possibly in the moist environment of a boat.
Finding a reliable 12v motor that can deal with this load is a major problem. There just aren 't many reliable 40amp 12v motors and they are expensive. Compare to the availability of standard 1.5kw motors and the 12v motors seem to be a rip off. You can buy a standard 1.5kw motor just about anywhere in the world.
Just about all the guys we have spoke to that run 12v watermakers run there engine whilst they are making water. The reason is two fold. Because the 12v watermakers make so much less water than a 220v system you need to run them twice as long as least. Whilst you are making water you are likely to be depleting your batteries unless you have a very large solar set up. Even if you solar or wind turbine can keep up with the watermaker load you are not charging your batteries so you still end up with depleted batteries on the day you run the watermaker. In my opinion, if you need to run the engine then a 12v watermaker was the wrong solution. 12v systems are inherently less reliable and complex when you start to use high amps.
The alternative would be to install a cat pump off the engine using an electromagnetic clutch and a pair of 40" membranes. This would give circa 170-180 litres per hour. The run time of the engine would be about half the time you would spend with the 12v system if you needed to run the engine to keep up with the battery demand and you would make more than twice as much water. The system would have no electronics or electrics apart from the power supply to engage the clutch. Have a look at the Echotec watermakers. They make a nice simple watermaker that i would have purchased if i had built my own on very similar lines.