Obtaining spatially separated, high-frequency water samples from rivers and lakes is critical to enhance our understanding and effectivemanagement of fresh water resources. In this paper we present an aerial water sampler and verify the system in field experiments. The aerial water sampler has the potential to vastly increase the speed and range at which scientists obtain water sampleswhile reducing cost and effort. The water sampling system includes: 1) a mechanism to capture three 20 ml samples per mission; 2) sensors and algorithms for safe navigation and altitude approximation over water; and 3) software components that integrate and analyze sensor data, control the vehicle, and drive the sampling mechanism. In this paper we validate the system in the lab, characterize key sensors, and present results of outdoor experiments.We comparewater samples from local lakes obtained by our system to samples obtained by traditional sampling techniques. We find that most water properties are consistent between the two techniques. These experiments show that despite the challenges associated with flying precisely over water, it is possible to quickly obtain water samples with an Unmanned Aerial Vehicle (UAV).