Dehydration as low as a 2% body weight reduction negatively impacts physical and mental performance.

“if you are under hydrated or dehydrated then there is a clear negative effect on your body and as I increase the level or improve the level of hydration things get better whether this are physical performance or whether this is mental performance in fact we know that a body weight reduction of as low as 2% via dehydration so imagine you're doing a about of exercise and you're sweating and you lose 2% of your body weight that alone is enough to reduce accuracy in performance so the classic study we talk about here was in basketball players so shooting accuracy so free throw shooting I think is specifically what they looked at um significant reduction in performance with as little as 2% dehydration”