How Do I Know If My Dog Has A Water Infection?

Have your dog examined by a veterinarian.  Usually bladder infections do not produce a color change or smell to prepuce or penis.  If your dog is inappropriately urinating or painful when he urinates it is possible it is an infection.
Black tissue can be related to a benign color change or tissue can turn black when it is dying from infection, lack of blood flow, or trauma.  Another concern I have is does your dog have a growth or tumor on the prepuce or penis that is the problem.  Especially intact males can develop sexually transmissible tumors (transmissible venereal tumors).
Your veterinarian will help diagnose the correct medical condition and prescribe appropriate therapy.
Do not give medication without consulting with your veterinarian.  Canine doses often differ substantially and not all human medications are tolerated by dogs.  Medication in dogs is done by weight so "one tablet" is not appropriate for all dogs.

I don't know much about water infection but the black on him is an infection. If your not going to breed him he needs to be fixed. It is common for some male dogs to have this problem especially if they are around other dogs (*females). He will need antibiotics and you want to prevent this again, get him fixed!

My bitch aged 11 is drinking more and is passing water more often but it takes her a while doing so