Pr Pross answers you

"Well...stress is generally related to negative feelings, but from a psychological point of view we know that there is good stress, or well-being, and bad stress. And we recently demonstrated in our studies that good hydration has a positive influence on stress. Well hydrated people generally report to be more happy, less focussed and more alert.  On the other hand, dehydrated people generally report to be less content, less calm, more confused and less happy. 

Consequently, we can say that good hydration has a positive influence on stress, and wellbeing. On the other side, dehydration has a negative influence on stress and induces bad stress. So, good hydration has an influence on stress. This is a fact."