I was just going to suggest the ocean spray cran juice too, Gothmum!
I have a glass every morning and night (besides water that's all I drink!) as I'm prone to thrush and apparently that and UTI can sometimes go hand in hand cos of the whole bacteria thing.
It's great as a prevention, apparently it makes the walls of your urethra and bladder all slimey so no nasties can cling to it.
If it's to strong for him you can dilute it a little with some water too. Poor bugger, hope he's ok soon! xx