investing water stocks

You've no doubt heard about the building scarcity of water. It's the reason savvy shareholders have been busy investing in water stocks.

Here's why.

Water may be everywhere but only 3% of it is fresh or suitable for drinking. Two-thirds of that is locked in glaciers and polar icecaps, which means less than 1% of the world's fresh water is available for human use.

That's the water found in lakes, rivers, reservoirs, and underground sources shallow enough to be accessed cheaply. Even still, much of that is polluted or otherwise unsuitable for consumption.

The water that's left is then used in agriculture and industry, and here's the kicker: It is divided between seven billion people... and demand is increasing all the time.

According to the United Nations, in the last century water use has increased at more than twice the rate of population growth.

Water has become so critical that Willem Buiter, chief economist at Citigroup, believes it will soon become "the single most important physical-commodity based asset class, dwarfing oil, copper, agricultural commodities and precious metals."

That may be hard to imagine, considering we can simply turn on the tap and get fresh water for next to nothing.

But it's true. There are myriad of factors-from population growth to climate change-putting a strain on the world's water supply and causing demand to spike.

We'll look at those factors and how investors can benefit from this growing demand by investing in water stocks.