[sailingdog]

Most of the ones that attach to the faucet aren't really a good idea for boats, since they require fairly high pressure to operate them. IMHO, you'd be far better off with one that was in-line, like the old NSA units, that install in the faucet's cold water feed line. These are generally lower pressure, but all the water that goes through them is filtered. One solution I've done for a friend's boat was to setup a second cold-water only tap that was filtered water.