Stranger things: the water

More than 45 institutions from Europe and around the world have joined forces in the Centre for Molecular Water Science (CMWS). The CMWS was officially opened at DESY on 26 February 2025. In close collaboration with the experts at the CMWS, PETRA IV will make it possible to investigate the fundamental properties of water with unprecedented spatial and temporal resolution.

Although we are constantly in contact with it, water has amazing properties that distinguish it from other liquids. These special properties are important for our lives - yet science does not understand all the details.

Strange things that water can do:

• Ice floats on water: Normally, liquids become denser as they get colder. But water is densest at 4 °C and expands as it cools further. This is why ice floats on lakes, which means that the water underneath does not freeze immediately and fish survive in winter. 
• Supercooled water: Sometimes water remains liquid even though it should freeze. For example in clouds, where it can still exist as drops at -30 degrees Celsius. 
• Water stores heat: It can absorb and release large amounts of heat. This helps to stabilise our climate - without water we would have extreme temperature fluctuations. 

How researchers want to solve the water puzzle:

Scientists are aware of the amazing properties of water. However, they do not yet understand exactly how water molecules ‘work together’ to create these phenomena. In particular, the invisible connections between the molecules, known as hydrogen bonds, have not yet been fully researched. This is where PETRA IV will help.

PETRA IV will track the dynamics of complex molecular networks such as aqueous solutions down to the nanosecond, 100 to 10,000 times faster than today - with maximum spatial resolution. According to one theory, water in its liquid form consists of two structurally and dynamically different components. PETRA IV could distinguish between these liquid states for the first time.