Water reaches its maximum density at around 39 degrees Fahrenheit. When water either cools or heats beyond this point, it becomes less dense. Although most ice floats on water, heavy ice is composed of an isotope of hydrogen known as deuterium and sinks as a result of its heightened density.
Water is the most common compound on Earth that is found in all three familiar phases of matter. Solid water is ice and crystalline in composition, while gaseous water is vapor or steam. A wide variety of substances are dissolved by water, which makes it a ubiquitous solvent. Water is essential to all life, and it represents between 55 and 78 percent of the human body in mass.