With incidents of severe water scarcity expected to rise substantially as the global population grows and fresh water supplies diminish, scientists are scrambling to come up with effective solutions to the pressing problem of increasingly limited fresh drinking water.

Over the past few decades, desalination has been all the rage. The most common method of desalination utilized today is reverse osmosis. Salt water is filtered through a semipermeable plastic membrane, which separates the ion particles (like salt) from the water, leaving potable water flowing out the other side. The problem is, reverse osmosis is costly and presents environmental concerns of its own—namely, what do you do with the leftover salt created during the process?

If you release the salt back into the water, you risk disrupting delicate aquatic ecosystems because of increased salinity. You could bury the leftover salt, but that's not a great idea, either. And while desalination plants produce fresh water, we have to burn a lot of energy to reap those rewards.

As part of a series of reports on global water issues, National Geographic explores some possible answers to these problems. Although modern desalination techniques are more energy efficient than older ones (boiling massive quantities of salt water and harvesting the steam for fresh water wasted tremendous amounts of energy), better solutions remain undiscovered. The article presents three potential alternatives to reverse osmosis, but a panacea eludes modern science.

With 1.8 billion people expected to live in areas of extreme water scarcity by 2025, and desalination plants expected to double their rate of output by 2016, we're on our way to figuring this out, but need to redouble our efforts nonetheless. Anyone have any groundbreaking ideas? Let's put this issue to bed.

Evidence suggests there is water on Mars. Maybe we can just zip up there and grab some?

Image credit: James Grellier