It could mean how much fresh water we have. Or how it's part of mother nature meaning what helps our planet to help us survive.
fire or earth
They are elements. Earth, Wind, Fire and Water are the four ancient elements.Then theres the chemical elements, which you can find out on a periodic table.
http://www.mp3raid.com/search/download-mp3/1802458/earth_wind_water_toy_box.html right click download and click on "save target as" and there you go
Wind can cause erosion of rocks and weathering and imagine the earth without water. Water helps plants and tress grow while cooling us off
They are from the United States of America