The origin of water’s anomalies has been a matter of long-standing debate. A two-state model, dating back to Röntgen, relies on the dynamical coexistence of two types of local structures—locally favored tetrahedral structure (LFTS) and disordered normal-liquid structure (DNLS)—in liquid water. Phenomenologically, this model not only explains water’s thermodynamic anomalies but also can rationalize the existence of a liquid–liquid critical point (LLCP) if there is a cooperative formation of LFTS. We recently found direct evidence for the coexistence of LFTS and DNLS in the experimental structure factor of liquid water. However, the existence of the LLCP and its impact on water’s properties has remained elusive, leaving the origin of water’s anomalies unclear. Here we propose a unique strategy to locate the LLCP of liquid water. First, we make a comprehensive analysis of a large set of experimental structural, thermodynamic, and dynamic data based on our hierarchical two-state model. This model predicts that the two thermodynamic and dynamical fluctuation maxima lines should cross at the LLCP if it exists, which we confirm by hundred-microsecond simulations for model waters. Based on recent experimental results of the compressibility and diffusivity measurements in the no man’s land, we reveal that the two lines cross around 184 K and 173 MPa for real water, suggesting the presence of the LLCP around there. Nevertheless, we find that the criticality is almost negligible in the experimentally accessible region of liquid water because it is too far from the LLCP. Our findings would provide a clue to settle the long-standing debate.

水异常的起源一直是一个长期争论的问题。可追溯到伦琴的两态模型依赖于液态水中两种类型的局部结构（局部偏爱的四面体结构（LFTS）和无序正常液体结构（DNLS））的动态共存。从现象学上讲，该模型不仅可以解释水的热力学异常，而且可以通过LFTS的合作形成来合理化液-液临界点（LLCP）的存在。我们最近找到了直接证据，证明液态水的实验结构因子中LFTS和DNLS共存。但是，LLCP的存在及其对水的性质的影响仍然难以捉摸，水的异常起源尚不清楚。在这里，我们提出了一种独特的策略来定位液态水的LLCP。第一，我们基于分层的两态模型对大量的实验结构，热力学和动态数据进行了综合分析。该模型预测，如果存在LLCP，则两条热力学和动力学波动最大值线应相交，我们通过模型水的百微秒模拟确认了这一点。根据最近在无人区进行的可压缩性和扩散率测量的实验结果，我们发现，对于真实水，两条线的交叉点分别在184 K和173 MPa左右，表明那里存在LLCP。然而，我们发现，在液态水的实验可及区域中，临界值几乎可以忽略不计，因为它离LLCP太远了。我们的发现将为解决长期辩论提供线索。