These British Berkefeld gravity filters are great. They allow you to perform high-quality water filtration on your counter top using gravity alone. The ceramic filters inside last for years, and need cleaning only every three months or so. They're pretty easy to operate too — you just pour water in the top half, it the water drips down the bottom half. After a few hours you have gallons of ready-to-drink water. Ceramic filters remove more than 99% of pathogens in water. You can read about them here.Other systems such as under-the-sink and on-tap designs, push the water too fast throught the filter for full filtration to occur.
Using this kind of filter you can get clean, drinkable water that is probably of better quality than most bottled water available.