Distilled water, an alternative to water filtration systems or bio-sand filters. A scientifically proven way of removing all the impurities in the water. DIY (homemade) solar water distillers or desalination devices can be made easily.
Eco-distillers
The latest innovation in distillers is an optimized version of existing solar distiller concepts.
Eliodomestico: An eco-distiller running on solar power
How it works
http://www.gabrielediamanti.com/projects/eliodomestico---how-does-it-work/
References and plans
http://www.gabrielediamanti.com/files/Eliodomestico%20references.pdf
Classic Eco-distillers
Can be made with cheap and easily available materials such as: plexiglass, plastic, concrete, etc
Source:
http://web.stanford.edu/~twmark/agua/engineering_solutions.htm
Full study available from the World Health Organization in the references on Wikipedia https://en.wikipedia.org/wiki/Distilled_water