众所周知，表面张力对液滴或水柱的形状及其演化规律起到关键作用，但由于流体力学模型的复杂性，一些常见的螺旋状水柱现象的具体机制并不明晰. 在这里，我们研究柱状射流的二维液滴模型，通过分析转动中二维液滴的离心势能、表面能、以及表面波振动的特征模式，解释了链状与带状水螺旋的形成原理. 理论模型表明，这两种水螺旋现象各自对应于一个普适的液滴形状“相变”前后的不同状态. 我们用简单的实验验证了此模型在一定参数范围内的合理性. 

 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.