3 people x 100 gallons each x 10 grains = 3000 grains a day. In my opinion, people who remain slim are slim not because they have strong will-power to resist extra calories, but because they have strong-walled healthy veins which can resist the incursion of extra salt water. In my experience systems that require you to remove the cartridge housing to change the filter requires much more work, and mess, than the "Kwik-Change" system available from the link below.