Although surface water on continental masses accounts for less than 1% of Earth’s water, rivers and lakes are an important source of drinking water as well as helping moderate local weather. Water distribution on land is also an indication of changing conditions on a global scale. One of the greatest global challenges of the 21st century is securing fresh water for the increasing worldwide population and for sustaining natural ecosystems. Geodetic monitoring of water level changes in rivers and lakes yield important constraints for hydrological models that can serve as decision support tools for water resource managers.