How common is the use of water purifiers in the West? Here in India, in my observation, most middle class and above families own a household water filter of some sort (electrical or otherwise) and routinely fill up bottles for drinking purposes. Drinking straight from the tap is something very uncommon.
It depends on a country. A lot of people think that just because it's from a bottle, it's safer. In many countries,the quality of bottled water isn't regulated,or not regulated as much as the tap water. I lived in 4 different countries in Europe and always drank tap water.My own country is one of few in the world, where tap water is supplied pretty much exclusively from underground sources,so no purified river/lake water.
A lot of people mention Brita filters, which is an activated carbon filter, however a lot of households would probably benefit more from limescale filters.