Water crises are the biggest risk facing mankind - here's why

When you look at the big picture, it's not surprising. In short, we don't have enough fresh water, and things are getting worse.

Four billion people already face severe water scarcity at least one month each year, according to a recent study. Supply will tighten as populations grow and demand rises for not only drinking water but also use in manufacturing, electricity, and more. At the same time, the world faces rising temperatures and many areas will suffer declining precipitation.

We've gathered some worrying insights on what's coming.