When water is at room temperature, its density is 998.23 kg/m3, which is only slightly less than the normal density of water at exactly 1000 kg/m3. The density of water is dependent on the temperature.
The major difference of density of water in relation to the temperature of the water is when the water goes from a liquid state to freezing. The water becomes less dense when it is frozen than when it is liquid. Water also become slightly less dense when it is heated up to a boiling temperature, but the difference is not as large as the difference when it is frozen.
One of the biggest examples of frozen water being less dense than liquid water is the occurrence of frozen pipes. Water is able to flow freely through the pipes without getting stuck. When the water freezes, it can become trapped in the pipes and can clog up all of the other water that is not frozen. This part of the pipe that contains frozen water has the possibility of bursting because the water has become less dense than it normally would be. This density issue is also the reason icebergs can float. They are less dense than water and will sit in the water instead of sinking.