I use a garden hose with a small shutoff valve on the end. If the valve closes tightly, loosen up the threads so it drips fast, or at most a small constant trickle of water. Then I open the valve to rinse.

: Use more water. I wet the boat down before I start, and have a bucket of
: water that I keep dipping the sandpaper into, and then rinse the boat off
: afterwards. If you can set up a way to have a constant trickle of water on
: the area you're sanding, all the better. The key is to keep the area
: you're working on wet. (The white residue is easy to deal with when it is
: wet -- it rinses right off. If you're getting a big build up of white
: residue, you're not using enough water.) I find that I can do the whole
: boat with one or two sheets of 400 grit paper.

: Julie Kanarr