This site shows great science experiments to show students how important conservation is. Although turning off water while brushing your teeth isn't going to solve the global water crisis, but it will bring it down to younger students level.
Water Will Be The Oil Of The Century: Fresh water needs exceed growth. World uses of freash water, by 2025 that would be Rain Barrels are a sustainable method of water conservation. And Nestle is draining groundwater reserves around the world
Possible school experiment to show importance of wetlands/riparian zones! This shows the importance of plants in our soil. Plants like trees and grasses help purify ground water. Without them the ground water gets polluted and harder to clean and drink.
Surprising facts about global agricultural water use: Infographic