Have yet to see any of mine drink water. Super juicy roaches I spose. My experience with reptivite so far is it smells and probably tastes disgusting. I think its meant to be mixed with something. Personally, I wouldn't do this, may turn them off to the water.
I would stick to dusting your feeders with the reptivite but if your wanting to give them extra calcium I would either put some in the cap of a gatorade bottle and leave in their tank or they carry liquid calcium that you can put in water although I have only seen 2 of my geckos drink their water but it might work.