I've had two PUR (now Katadyn) watermakers, and my next one will be something else. They do require significant maintenance, and since Katydyne took over, the prices, especially for spares have increased significantly.
Example--the main bearing in the drive went out, and I asked Katadyn for a replacement. Their response was that I wasn't supposed to be able to take the drive apart, they didn't carry the new bearings, and I needed to buy a new drive for 2000 euro. It took quite a bit of internet surfing, but I eventually found the bearing for $20.
Example--the pump piston rod, which is a 4 inch piece of stainless about 3/8 inch in diameter--over $100.