Water is densest as liquid. Specifically at 4 degrees Celsius. Other elements have largest density when they are in their solid state but for water that is not the case. Solid water state (better known as ice) is around 10% less dense than water in liquid state.
It is also interesting to know that water density is increasing as temperature is lowering up to 4 degrees (which is point of largest density) from which further decrease of temperature will start making water density decrease.