When water is heated, it expands, or increases in volume. When water increases in volume, it becomes less dense. As water cools, it contracts and decreases in volume. ... For samples of water that have the same mass, warmer water is less dense and colder water is more dense.

How does water expand when heated?

The warming of Earth is primarily due to accumulation of heat-trapping greenhouse gases, and more than 90 percent of this trapped heat is absorbed by the oceans. As this heat is absorbed, ocean temperatures rise and water expands. This thermal expansion contributes to an increase in global sea level.

Does water expand more when heated or frozen?

Long Answer: Normally, things expand when heated and contract when cooled. Water is an exception to this rule. Even though water does expand when heated and contract when cooled at most temperatures, water expands when cooled and contracts when heated between 4 degrees Celsius and 0 degrees Celsius.