Well its definitely true, that higher quality water regenerates more stamina per hunger, but the way it works should be vice versa.
While q10 water restores 5% Stamina per 2% (or so) hunger, q13 restores 7%. Now why is this bad? Because higher quality water will restore even more %, but you never get the last missing %.
For example with q10 water you can only restore until youre <5% under 100%, you have to wait the rest of the time. And if quality 30 water will restore 10%, you will have to wait 9% in the worst case.
So my suggestion is to make water always regenerate 5%, but take less hunger the higher its quality is.