Did you check the supplier's site? Sometimes they give tips on the best way to incorporate it. I've only used oil soluble so I can't tell you much about it. Although, there have been discussions on the forum about it.
I have an order I'm gonna place at Rustic Escentuals and all they have is water soluble. Says to mix with water. I just wanted to be sure it will work just like the oil soluble in my CP soap for whitening.