I use a portable deionized water system to wash my 23’ Cape Cruiser (C-Dory) and it works amazingly well. I also use it on a travel trailer and on our house windows. Simply do a normal wash and rise off the soap and gunk using water from the system, which is connected to a normal pressurized outlet. I then simply let the boat (or windows) drip dry and it dries completely spotless. I live in Las Vegas and we have amazingly hard and mineral filled water (including from rain, as well as the water in Lake Mead) so washing anything with tap water, like the boat or a car, leaves tons of hard to remove water spots unless instantly and concurrently dried by hand. Washing used to be a chore but not anymore. I know this sounds like a commercial, but it has been my experience. I’ve noticed 3 drawbacks to the system. One is the initial system cost. Another is the weight, even of the small one. It’s relatively heavy and bulky to move around. And another is the continuing cost of the resin refills for the 2 resin containers. Each refill costs roughly $50 and includes both containers, and I get about 4 washes before I start to notice some spotting. The longer I go without a refill the more spots I’ll start seeing. There are many systems out there on the market, including from Costco. The one I have is the Spotless DIW-10. While I wash my boat on the trailer at my house, I don’t know why it wouldn’t work just as well in a marina.