When you think of places where girls have to walk for hours to carry back water, you might tend to think of hot, dry regions of Africa. But water shortages can happen anywhere in the world—from remote villages in Albania to cities right here in the United States. Schoolchildren learn that water covers 70% of the planet—it sounds so plentiful. But the fresh water we drink and use in our homes and on our farms only makes up 3% of the world’s water. And most of that is unavailable—locked up in frozen glaciers or otherwise inaccessible. So providing clean water is more difficult than it might sound at first glance.…