AbstractOrdered structures in liquid water are discussed. Raman spectral changes of water in the temperature range −23°C to 45°C are analyzed with multivariate curve resolution with alternate least squares (MCR‐ALS) and hypothetical addition multivariate analysis with numerical differentiation (HAMAND). Three forms of water, destructured hydrogen bonded (DH) water, structured hydrogen bonded (SH) water, and nano‐ice, are identified. Formation of nano‐ice is shown to cause the density maximum anomaly of water at 4°C. The size of nano‐ice at −13°C is estimated to be 2–4 nm. SH water corresponds to one unit cell of hexagonal ice structure. The SH/DH ratio is an indicator of “structurality,” which is useful for microscopic understanding of liquid water. The existence of nano‐ice in cold water raises a fundamental question “Is cold water a genuine liquid?” Further study on the size of nano‐ice will give a clue to understand how water freezes or does not freeze.