In our occasional series, Celebrities Doing Green Stuff, we take a look at the environmental causes and activities that celebrities have decided to champion. Today's celebrity is Matt Damon. His cause -- water! Water management is a growing concern throughout the world, from drought-stricken California to water-poor Yemen and polluted water in Brazil. Water is a resource that, when polluted or simply missing, causes widespread suffering and environmental refugees. Did you know that over 600 million people in India alone (that's double the U.S. population) don't have access to a toilet? Did you know that the mosquitoes that carry the Zika virus breed in polluted areas and fly during the day (very different from malaria mosquitoes)? Did you know that the nation of Yemen doesn't have any rivers, so they take all of their water from groundwater -- a source that can be quickly depleted? Take a look at what Matt Damon is doing and how you can help.