In many parts of the world, water is at risk of over-exploitation and contamination. To protect it, scientists study its most invisible details with the help of nuclear technology. The IAEA supports scientists around the world on isotope hydrology - nuclear techniques that are used to determine the quantity and quality of water supplies. The IAEA sends experts to the field and train local hydrologists in the use of these isotopic techniques. Based on data such as the recharge rate of water in aquifers, policymakers are in a better position to establish rules for the use of water for drinking, agriculture and industry.