Can someone tell me what type of snake this is?

my friend gave me a snake it was white with brownish red patches with black borders.every time i picked it up and it will bite me. i put it in a fish tank with food (fish),logs,mulch beding,water,rocks,caves,and a heating lap it loves it but its not white any more its brown with brown patches and a black border the under side is black with whitish gry dots and a tan line running down it its chin is white.me and my mom think its a northern water snake but where not too shore.