"Several diving biomechanics studies examined the velocity of divers as they enter the water and reach various depths. People diving from boards and decks hit the water at about 15 feet/sec. Estimates of the point where downward motion ceases is between 12-15 feet, although other some place the depth for absolutely safe diving at 18-20 feet." "It has proved surprisingly difficult to determine the depth of water required for safe diving. The recommended minimums cover a wide range, from the American Red Cross and FINA (Federation Internationale de Natation Amateur) estimates of 3 feet to the Australian Diving Association estimate of over 9 feet. SportSmart Canada recommended diving only when the depth is twice diver height." "It is important to note that such estimates are merely "standards" and are not based on any physical, empirical science." "Lastly, safe depth depends at least partly on dive angle and technique. It is likely that short of making pools so deep that all vertical motion ceases, maybe 15 feet, there will never be an absolutely safe depth for all divers." Source and further information: http://www.visualexpert.com/Resources/divingaccidents.html