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.
The latest innovation in distillers is an optimized version of existing solar distiller concepts.
Eliodomestico: An eco-distiller running on solar power
Can be made with cheap and easily available materials such as: plexiglass, plastic, concrete, etc
Full study available from the World Health Organization in the references on Wikipedia https://en.wikipedia.org/wiki/Distilled_water