Because it is a safe and healthy option, and it is also much cheaper than bottled water. Tap water in Europe and North America is subject to rigorous regular checks. TAPP filters remove substances from the distribution network (such as heavy metals, if you have old pipes), as well as chlorine, which is often the source of bad tasting water. Moreover, filtered tap water is more environmentally friendly than bottled water. The CO2 footprint of bottled water originates not only from its production, but also from its transport and distribution. And last but not least, TAPP tap filters are much more convenient, as you no longer have to carry heavy bottles of water from the supermarket to your home.