Stay far away from Jem. I have a 24/7 as a backup hazer. I should have a backup for this POS. I replaced every part in it with brand new factory parts. Used it 3 times, and the heater core broke down again! And yes, it is water based.
My main hazer is a DF-50. There are not enough good words in the English Dictionary to talk about this thing. Its great. Oil based, but I believe you can actually buy a water based-solution for it (through either Reel EFX or CITC). I've never tried the water based stuff.