Rice Water is the water you have from boiling rice. Get some of the long-cooking, regular rice and boil it for half the time recommended (usually the total cooking time is 20 minutes) scoop out your water and discard the rice. You can add this about a 1/8 of a cup at a time to the moist food.
When you say the poop is really foul smelling ... this leads me to ask if your vet screened for coccidia or giardia? They sometimes do not show up in a normal fecal sample - if this persists, you may ask your vet about it.