Answer: Water is less dense as a solid (ice) than it is as a liquid.
When water freezes into it's solid form that is ice, it's molecules attain more stability in it's hydrogen bond. As, these hydrogen bonds attain their position rather remaining free as seen in liquid water. Due to this type of hydrogen bonding the ice attains a compact structure. The hydrogen molecules in ice are separated from each other, which were earlier closer to each other. Hence, structure of ice reduces it's density as compared to liquid water. Therefore, the property of water which allows icebergs to float is water is less dense as a solid than it is as a liquid.