My dr. said that my labs show me as looking deydrated but i drink more than 75oz of water a day. how is that possible?

Need more details: We need to see your actual blood tests. Maybe you are not dehydrated. An elevated BUN can be a sign of dehydration but can also be a sign of other medical problems, including a bleeding stomach ulcer, liver problems, congestive heart failure, other med effects, or even just an aggressive low carb/high protein diet. Check out this link: http://emedicine.medscape.com/article/2073979-overview

Volume depletion: you might have excessive sweating. High temperature at work or in your surrounding ,excessive exercise might contribute in fluid loss and cause dehydration. Some medical conditions like uncontrolled diabetes( causes excessive urination) ,diabetes insipidus and some kidney diseases may contribute in dehydration. some medications may cause dehydration or renal dysfunction.(like diuretics and NSAIDs)