The sensors in water surface sensor networks are sparsely deployed, which means the distance between sensors is generally larger than the sensors' communication radius. So, it is difficult for sensors to aggregate their data by multihop routing. If water surface mobile sink is to be used to collect the sensors' data, its path forming method is a key issue. In this paper, the Voronoi diagram and dominating set theory are introduced, and a path forming method called path forming Voronoi diagram dominating set (PFVD) for water surface mobile sink is proposed. First, the water surface sensor network structure is converted into a Voronoi diagram and the adjacent sensors' data can be collected at the generated Voronoi vertexes position. Second, the dominating set theory is used to compute the minimum set of Voronoi vertexes that can gather all the sensors' data. Finally, based on the minimum set, the final path for mobile sink is formed. Theoretical analysis and extensive experiments demonstrate that PFVD has the advantages of short path and balanced energy consumption in different scale networks.