A question: if we can fly to the moon, can we make a 1$ water filter for people to use in their homes? And, if the answer is yes, why haven’t we yet? This is one of my favourite things: the quest for extremely affordable point-of-use water filters.
There are some hopeful developments. After Hindustan Unilever had introduced their [http://www.pureitwater.com/index1.htm Pureit water purifier] at a price level of 30$ for a very well-designed and effective water filter, protected by 21 patents and using 5 water filtration steps, Tata Company recently introduced their [http://www.tataswach.com/ Tata Swach water purifier], at 20$, with 1 filtration step, but equaly good-looking. And we already had the [http://www.vestergaard-frandsen.com/lifestraw.htm -family-1-0 Vestergaard Live Straw LifeStraw Family1.0] filter, also at $20$. In the open source hardware corner, we have the [[Concrete_Biosand_Filter|biosand filters]], and [[Ceramic_pot_filter|ceramic pot filters]]. Lots of good stuff.
These filters all use some combination of microfiltration, disinfection and adsorbtion. Microfiltration simply blocks bacteria from passing through the filter by using a highly porous material in which the bacteria basically get lost. Disinfection, for example using chlorine, kills bacteria and other pathogens using chemical means. Adsorbtion, finally, uses carbon to adsorb molucules, improving taste, smell, and colour of the water. Not all filters use all three, and this is where the main differences in quality lie.
