Water is a polar molecule that forms hydrogen bonds between its molecules, giving water unique properties. It freezes at 0° Celsius and boils at 100° Celsius. Water also has a high specific heat capacity, which means it requires a lot of energy to change its temperature. This allows water to moderate temperatures and transport heat around living things. Water can also dissolve some materials like limestone through the formation of carbonic acid when water interacts with carbon dioxide in the air, allowing it to slowly erode rocks and form cave systems over long periods.