It is well known that surface tension plays a crucial role in determining the shape and evolution of a droplet or a liquid jet. However, the specific mechanisms of some common “water spiral” phenomena remain elusive. Here, we study a two-dimensional droplet model for a liquid jet to explain the formation of water spirals by calculating the surface energy, centrifugal potential, and surface wave eigenmodes of a vibrating and rotating droplet. We find that the commonly-observed chain-like and belt-like water spirals correspond to states before and after a phase transition of the droplet^,s shape, respectively. The rationality of the current model within a certain range of parameters is justified with simple experiments.