My boxer has lately been peeing his crate

Question
Hello my 18 week old boxer has been peeing his crate lately while I leave him alone at home.  I received him when he was 10 weeks old and house trained him from the start. He was excellent with only a few incidents in the house and his crate.  
He sleeps on another little bed in my room when we go to sleep at night and does not have the habit to pee his bed then.  It has only started to happen a couple of weeks ago in his crate during the day and I only leave him alone for between 2-5 hours max.
I always take him out to pee before putting him in.  I have been told that a pup can hold it in for (the age in months plus 1) so 5 hours.  
He is a very happy puppy and we visit the vet regularly as she is just around the corner. I walk him everyday and he has many playmates at the park. I always leave him in his crate with his favorite toys to play with and of course water, but I feel he is doing it out of spite.
Some people advise to reduce his water supply. I refuse to even though he spills most of while he is in there.  I wash his bed everyday and clean up the crate, but it is just frustrating knowing that he didn't used to do it when he was younger. He had a minor urine infection 4 weeks ago and he only did a pee a couple of times accidentally inside. The vet said it would be gone in a week when he finished his medication. He shouldn't have any infections as he wouldn't only be peeing in his crate and not only when I'm not home.

Hope you can help me and my little buddy :(

Answer
Before trying to go any further with the issue, let's get the vet to check him again to be positive the urinary infection is really gone or that he still has it- as some antibiotics might not work completely on different dogs (as in people) or didn't completely kill off the infection, thus allowing it to re-fester.

After being tested, let me know the results and we can work on his peeing in his crate.

In the meantime, does he hold it all night (typical 8 hour night) without incident? If so, he should be able to hold it 2-5 hours.

If he does indeed spill his water while in his crate, there is no reason to leave water for him.

I would check into a bottle-type water dispenser that attaches on the crate made specifically for dog crates. But, since being so young, I would be leery of him chewing on the water bottle dispenser while you are away.

Get the vet to check his urinary tract first to be sure you aren't dealing with that issue.