At 0 degrees Celsius, water exists at its freezing/melting point, meaning it can be in both the solid state (ice) and the liquid state simultaneously. This temperature represents the phase boundary where water transitions between liquid and solid phases under normal atmospheric pressure. Specifically:

• At 0°C, water and ice coexist in equilibrium; molecules in liquid water can lose energy and become solid ice, while ice can gain energy and melt into liquid water

• This temperature is often called the freezing point of water, where the phase change occurs without a change in temperature until the transition is complete

• The triple point of water, where solid, liquid, and vapor phases coexist, is very close to 0.01°C, but at standard atmospheric pressure, 0°C marks the equilibrium between ice and liquid water

In summary, at 0 degrees Celsius, water is at the threshold between solid and liquid states and can physically exist as both ice and liquid water simultaneously.