I would be surprised if you could find a specific figure, but it's highly soluble in water. (As are most amine salts.)
Although most of the MDMA molecule is non-polar (relatively), the non-polar interactions (van der waals forces) are still relatively weak compared to the attraction between the amine and water, allowing water molecules to latch onto and drag apart MDMA hydrochloride crystals fairly easily. (The fact that it's sold as an amine salt is important to producing that water solubility, since the protonated R-(NH2+)-R is a lot more polar than R-NH-R.)