They're probably looking for false, but to be honest, I use it in my writing sometimes. It depends on the setting and character, or it should be specified as slang in nonfiction writing.
1. To prevent drought because South Africa is considered one of the 30 driest countries in the world.
2. To store rainfall (to prevent drought).
3. Dams change daily flows by releasing water as a reaction to demands for irrigation, energy, etc.
