Why are bedsores less likely to develop the body of a hospital patient if the hospital provides the patient with a water bed rather than a regular bed?

Bed sores are caused when pressure on the skin cuts off blood circulation, because there is no/little blood flow to the skin, the skin begins to die, resulting in bed sores. The pressure is more evenly distributed over the surface of the skin in a water bed, allowing blood to flow more freely, resulting in far fewer risks of bed sores.