I have looked and looked and I can find nothing on the water solubility of THC and THCA. I even found the MSDS sheets (yes, they now have MSDS sheets on cannabis. LMAO) and the data for water solubility was "No Data Available".
I did find one post in a forum where someone claimed it was .3% but he didn't have any footnotes so it could have been conjecture, opinion or plain bull.
In my reading I did find something odd. Several laboratories claim that during the drying and curing process heat and light help to convert the THCA to THC. Why do we all dry our pot in a cool dark place?
Found in the trichomes, Tetrahydrocannabinolic acid (THCa) is the acidic precursor to THC, which actually exists in only minute quantities in the living plant. In living cannabis, THCa is the most abundant cannabinoid and terpenoid, potentially reaching over 30% of the dry weight of any cannabis plant. Immediately after harvest, the THCa begins to be converted into THC, a process quickened by exposure to heat and sunlight.