A positively charged nitrogen on the amine group is not as likely as a positively charged carbon on the ring. I believe its easier for a carbon to give up an electron than it is for a nitrogen, especially since the carbon is in a ring. This will leave the carbon two away from the amine group attachment site positive. The O in water can then attach itself to the carbon, leaving a proton as the leaving group.
Not totally sure since I took ochem a long time ago, but I believe the summary above is correct.