Book excerpt: Water is one of Earth's hot environmental topics. The scarcity of clean drinking water will have dramatic consequences for humanity in the 21st century: water disputes could spark regional conflict, while increased desertification and drought could affect world food supplies and the future of farming. Not a Drop to Drink conveys a clear message to young readers about this precious commodity and our urgent need to conserve it. National Geographic supports K-12 educators with ELA Common Core Resources. Visit www.natgeoed.org/commoncore for more information.