Many people prefer a cold glass of water compared to the cool to room-temperature water that comes out of the tap (Hence the refrigerator for cooling). Filtering at the individual level is typically done for flavor, because depending on where you live, while the water is probably safe to drink (assuming HN readership demographics), it may or may not be particularly pleasant. Even here in the Bay Area, where we have that sweet, sweet Hetch-Hetchy water, I know people who live in buildings with pipes bad enough that they filter their water.