Water is one of the most familiar substances on Earth. We drink it, bathe in it and sail across it. Yet, after centuries of study, scientists are still scratching their heads over its strange behaviour.

Almost every liquid becomes denser as it cools. Water does too — but only up to about 4°C. Cool it further and it starts expanding, which is why ice floats. Water also stores heat unusually well and behaves oddly under pressure. For decades, scientists have wondered whether these quirks have a common explanation.

Now, researchers say they may have finally found evidence to settle a long-debated idea: Water constantly flips between two microscopic structures — a high-density and a low-density form. The trick was in persuading artificial intelligence to look where humans couldn’t.

Researchers at the City University of Hong Kong simulated the movements of thousands of water molecules, generating millions of data points. Instead of telling an AI system which patterns to search for, they let it teach itself — a technique known as unsupervised deep learning. The AI sifted through the mountains of data and picked out signatures that scientists say support the “two-state” model of water.

According to the researchers, AI accomplished in about 18 months what may otherwise have taken years of painstaking analysis.

If the findings hold up, they could help explain why water has puzzled scientists for so long. It would also serve as yet another reminder that even the most ordinary things can hide extraordinary secrets — provided someone knows where, and how to look.

Published on June 29, 2026