This marina is way out in the sticks, so the water supply is a well. It's the same water I wash the boat with (and my last boat), but I've never seen any mineral stains or residue.
September is the absolute worst. I scrubbed the topsides clean and went back after three days. Our former boat and all the other boats on my pier looked like the world's biggest black and white Jackson Pollock canvas. People have owls, CDs hanging from fishing line, fake snakes, and all sorts of other gadgets...nothing passive works. When people are around, the birds leave.
If the impact sprinkler doesn't work, I'm thinking Tesla coil... lol