Since deuterium is chemically identical to protium (normal hydrogen), heavy water generally behaves similarly to normal water; heavy water looks, feels, and tastes almost exactly the same as normal water. However, because a molecule of heavy water weighs more than a molecule of normal water, it freezes and boils at a slightly higher temperature than normal water. (Heavy water freezes at 3.8°C and boils at 101.4°C, as opposed to 0°C and 100°C for normal water.)
Most living things cannot survive solely on a supply of heavy water. Many of the chemical reactions that occur in living things require absolute precision, in both amount of chemicals and the timing of their movement around various tissues. Heavy water, with its greater weight and, by extension, momentum, does not allow these reactions to take place. Thus, while heavy water is not poisonous, it cannot support life on its own.
By far the largest source of heavy water is from Earth's oceans. A small percentage of the water in the oceans is heavy water. Heavy water plants simply pump in seawater and distill the heavy water from the normal water.
Heavy water has a high neutron opacity, which means that it can absorb a large amount of neutrons without major damage to its chemical structure. During World War II, the German Nazi government used heavy water to moderate their nuclear reactors in their experiments to try to develop an atomic bomb. However, a raid on a heavy water plant in Norway greatly hindered the German efforts. Beside this, the Americans working on the Manhattan Project learned that graphite could moderate nuclear reactions much more efficiently than heavy water, and it had the added benefit of being a solid, making it far easier to handle.