Dehydration Results In Lower Blood Pressure And Slows Bodily Processes. Active individuals should be aware of the acute effects of dehydration on performance. With just a 2% loss of water in the body, heat regulation becomes impacted. With a 3% drop in body weight from water loss, muscle cell contraction is impacted. And at 4% loss, there is 5-10% reduction in overall performance that can last up to 4 hours.