Bracing myself for ridicule from the water filtration geeks in the group, but I use the filtration machine outside my grocery store, filling five gallon Sparkletts-type bottles. I use it only for ice cubes, when I want a glass of pure water or when I want a cup of hot water immediately (my water dispenser has both hot and cold water). If I'm making something where the water is just an ingredient, I use tap water. As a bonus, I got the water dispenser from Craigslist for $30, and it produces very hot and very cold water. It's the old school style that everybody at the office wastes time standing around talking about the football game. I couldn't be happier. I go to the grocery store to do a water run about every three months.
The filtered water from the machine tastes just fine, good, in fact, and it makes crystal clear ice cubes. It costs .25 per gallon, and I dunno, maybe Britta filtered water costs less, but at the rate I use filtered water my 10 year loss of $$ as compared to using a Britta will proably be less than $50.