when i was young i boiled down some already very thick black bong water and smoked the residue, needless to say thc is not water soluble and i got sick. all your gonna do is nasty up the dirt, even if it had thc your plant can't utalize it in any way. when your plant is old enough to handle it, (3-6 weeks) go with some high nitrogen fertalizer, be carefull not to use to much or you will burn all the leaves off. good luck