You've said they were not drinking well with the medicine in the water, and I think you said they weren't eating well either.
You could try mixing some water with some of their usual food, and see if they like that. It can cause them to get more food and more water. (If you're doing any medicine in the water, use the medicated water when mixing with the food.) Do a small amount to see if they like it, and make sure you don't serve so much it has a change to spoil.
Won't cure any underlying condition, but helps stave off dehydration and/or starvation while they're not feeling well.