Physicists Just Discovered a Second State of Liquid Water

We think we know water. It covers two-thirds of our planet, makes up about 60% of the human body, and is essential for life as we know it.

But what if we’ve been missing something fundamental about its nature all along?

A team of physicists has discovered that when water is heated to between 40°C and 60°C (104°F and 140°F), it appears to undergo a hidden transformation—shifting between two different liquid states.

This isn’t just another quirk of water’s already bizarre behavior. It could fundamentally change how we understand everything from biological processes to nanotechnology.

And yet, despite its importance to life, water remains one of the most mysterious substances on Earth.

Water: The Rebel of the Periodic Table

We take it for granted, but water breaks nearly every rule in the book.

Unlike almost every other liquid, its solid form (ice) floats on its liquid form.

It has an unusually high surface tension—only mercury beats it.

Instead of contracting when it freezes (like most substances), water expands.

Its boiling point is oddly high for such a small molecule, defying the trend seen in other similar compounds like hydrogen sulfide (H₂S) and hydrogen telluride (H₂Te).

Physicist Philip Ball, writing for Nature, put it bluntly:

“No one really understands water. It’s embarrassing to admit it.”

And now, new research has deepened the mystery.

A Strange Phase Shift Hidden in Plain Sight

An international team of physicists, led by Laura Maestro from the University of Oxford, decided to take a closer look at water’s physical properties as it was heated.

They measured:

Thermal conductivity (how well it conducts heat)
Refractive index (how light bends when passing through it)
Electrical conductivity
Surface tension
Dielectric constant (how an electric field spreads through it)

The results were astonishing.

Each property shifted at a different temperature, all within the 40°C to 60°C range.

The researchers concluded that water was transitioning between two distinct liquid states—a property that has never been observed before.

Some of the key crossover temperatures they recorded:

Thermal conductivity shift: 64°C
Refractive index shift: 50°C
Electrical conductivity shift: 53°C
Surface tension shift: 57°C

Why Does This Matter?

This discovery suggests that liquid water may not be a single, uniform substance, but rather a dynamic interplay between two different liquid states.

And this could explain why water behaves so strangely compared to other liquids.

But before we get too carried away, let’s pause.

Because this discovery flies in the face of what we thought we knew about water.

Wait, Two Liquid States? That Shouldn’t Be Possible

Here’s the thing: water isn’t supposed to work this way.

We’ve been taught that a liquid is a liquid—its properties might change gradually with temperature, but it doesn’t suddenly “switch” into another kind of liquid.

Yet, that’s exactly what this research suggests.

To understand what’s happening, we need to talk about hydrogen bonds—the weak forces that hold water molecules together.

The Role of Hydrogen Bonds: Order in the Chaos

Water’s weirdness comes down to its hydrogen bonds—the temporary links between its molecules.

These bonds are:

Weaker than the internal bonds holding each H₂O molecule together.
Constantly breaking and reforming, lasting mere fractions of a second.
Responsible for many of water’s unique properties, like surface tension and expansion when freezing.

Physicists believe that at certain temperatures, these hydrogen bonds rearrange in a fundamental way, leading to a new liquid structure.

As Ball puts it:

“Everyone agrees that fleeting hydrogen bonds set water apart from other liquids. But that’s where the consensus ends.”

In other words, scientists still don’t fully understand what’s happening at the molecular level.

Why This Discovery Matters for Science and Medicine

This breakthrough isn’t just theoretical curiosity—it could have real-world consequences in fields like biology, nanotechnology, and medicine.

Impact on Biological Systems
Water is the medium of life.

If it behaves differently at certain temperatures, it could affect how proteins fold, how cells function, and even how medications dissolve in the body.

Implications for Nanotechnology
Nanoparticles—tiny materials engineered at the atomic level—are often suspended in water.

Their behavior at different temperatures could be influenced by this hidden phase transition.

Better Understanding of Water in Space
Since water is common in the universe, knowing how it behaves under different conditions could help us understand extraterrestrial environments—from Europa’s subsurface ocean to Mars’s ancient water reserves.