Barbara, I'm glad to hear that Tigris is making larger pee biscuits. Hopefully you'll be able to get him to drink enough water. What kind of food do you feed him? If he only eats dry then maybe you should start feeding him some dry mixed with wet food since wet food has a lot of moisture in it. This way he won't need to drink as much water.
My cats are on the prescription food by Royal Canine. It's the S/O formula and both Storm and Sunny eat dry and also dry and wet food mixed together. Cirrus and Sky prefer the dry. Now both Sunny and Storm are hooked on the wet stuff. This food also makes them drink more water and pee a lot more too. I don't mind as long as it keeps them all healthy and happy. Good luck.