Groundwater is an important resource and needs to be protected from contamination. Using age dating, we can determine how connected groundwater is with the surface of the earth and because of this, just how vulnerable it may be to contamination. We will show examples of the Alameda Creek watershed (Livermore Valley) and how surface water infiltrates the ground to become groundwater. We can study the formation and movement of groundwater using age dating. The radioactive decay of tritium (3H, half-life = 12.4 yr.) to stable helium-3 (3He) can be used to accurately tell how long the water has been underground. By measuring groundwater ages, we can see where and how fast the groundwater is moving. Areas of young groundwater (less than a few years old) locate zones that need the greatest protection from surface contamination. Careers in water resources include many disciplines. A mixture of geology, chemistry, biology, physics and engineering forms the backbone of the field. Delivering water to people is also a business. Projects need plans and budgets, information has to be communicated, and many people have to be brought together in decision making. Sample collection and monitoring of the environment is a large effort. Construction and maintenance of increasingly complex equipment requires people with broad technical training. Careers in water resources can be rewarding, fun and extremely important to society. Everybody likes clean water! This is the second presentation in this year's Science on Saturday lecture series. The series is co-hosted by LLNL's Science & Technology Education Program and Sigma Xi.