We were sooo done with bottled water from all the various charter trips we had that when we got our boat we put big bucks into a Seagull purifier. To this day we think this was the best ever product we bought for the boat. Not cheap, but we cherish this THE most among all our other do-dads. This system simply has an additional faucet off of our sink.
Seagull IV X-1F Purifier with Faucet - Water Purifiers and Water Micro Filters - General Ecology