I believe they have both. The need for both really depends on your area. If you have decent city water that come into your house, but your pipes are old, that obviously can effect the outcome of the water. Just as if you have bad water coming into your house, and it is ran through the hot water tank, it sometimes improves the quality by heating. It's a weird situation. Especially when you hear news that the water supply is filled with so many drugs and pollutants. We only use tap for showing, and cooking (if the water is going to be boiled). Otherwise, I use my Brita water, especially for coffee and tea. You'll notice a difference in quality the first time you use it.