I do not think there is any formula but you can find loads of literature published by University of Cape Town, South Africa. I believe the bottom line is-drink to thirst
-- Kind Regards, Dr.Tvisha Parikh Masters in Sport and Exercise Medicine (UK), M.B.B.S.(Mumbai) http://in.linkedin.com/pub/dr-tvisha-parikh/8/385/7b9 +91-8056140925
