Tommy , does your 5 gallon a day estimate include bathing or is that just drinking , cooking , washing , etc ? I am considering another more tanks for our boat , is the reason I ask. Glenn & Joanne Dean River Rats There are a lot of water filters out there, and a few are really good. But, if I only had 100 gallons, I'd be a lot more worried about supply. I'd think that most people use about 5 gallons each per day, over any period of time. That would cap your long range cruising plans to about 10 days. Tommy