Recent encounters of rhyolitic melts during drilling in Hawaii and Iceland reflect assimilation or derivation from their shallow hydrothermal system, because they all are partially made of oxygen and hydrogen derived from meteoric waters. Therefore magmas must be derived by melting of hydrothermally-altered crust and interact with the hydrothermal halos around magmatic intrusions. We present a numerical model that explain water behavior which suggests that water can be added to magmas in minor <1wt% quantities and this affects rhyolitic magma behavior in the crust next to the shallow hydrothermal systems. We also suggest that shadow rhyolitic magmas in the crust convect.