Pure Water
With approximately 70% of our physiology being made up of water, the purity and nutrients contained in it is of quantum importance. Drinking water from a source that is clean and provides trace minerals is one of the most health promoting activities you can undertake. However, people are still drinking inferior sources, such as tap, bottled, or poorly filtered water.
The absolutely best source of water is from a spring that has been proven to be clean of environmental contaminants. It is highly oxygenated, mineralized, and easy to absorb. In fact, it is what all water filters try to mimic, as it is the premiere source.
Failing that, get a good water filter that removes unfriendly contaminants, which will be a low cost and profitable investment over the course of their lifetime. See the first source below for Your Guide to Drinking Water.