First- THC is NOT soluble in water! You need alcohol or fats or oils in it to dissolve the THC. THC is NOT the only chemical in cannabis, and some ARE water soluble.
Second -here's an article on it (Granny always has an article!)
Cannabis tea revisited: A systematic evaluation
Cannabis tea revisited: A systematic evaluation of...[J Ethnopharmacol. 2007] - PubMed Result

Third, here's some alternative recipes, if you decide to try something else-
International Cannagraphic Magazine Forums - Cannabis Recipes

Enjoy! - Granny:hippy: