David, As with many things there is no absolute. Survival manuals will give 3 days max without water, which isn't very reassuring to somebody looking at their watch as 71 hours 58 minutes 33 seconds ticks by. It truly depends on the individual physiology, level of activity and environment. Many people will reference the P.I.R.A. hunger strikers and the length of time they lived. What people do not understand are the volunteers who were ordered off the strike suffered permanent health problems including loss of vision, deafness, motor coordination etc. So always start the day hydrating yourself with plenty of water and never pass on the last slice of pizza. At your age you need it anyway <img src="/images/graemlins/grin.gif" alt="" />