Ask a Vet and Get Your Veterinary Questions Answered.
Is he urinating?
If so, are the spots of urine of a normal size for him?
Has he urinated outside of the litter box?
If he is spraying, then you will see spots of urine on vertical surfaces such as curtains, walls, and chairs, as well as spots at the base of these things.
The blood in the urine, the inappropriate elimination (urinating outside the box), and urinating smaller amounts than normal indicate cystitis (inflammation within the bladder) possibly due to infection.
The biggest risk of cystitis in a male cat is obstruction of the urethra. A plug of crystalline material can block the outflow tract of the bladder making urination impossible. This is a life threatening emergency which can result in kidney failure and/or bladder rupture.
For tonight, monitor him to be sure he continues urinating. Encourage drinking, as you've been doing. You can also offer canned food, as this is 70% moisture. The extra fluid will help to flush out his urinary tract. Do NOT give any over the counter medications, as cats don't metabolize many drugs very efficiently and the wrong thing can be deadly.
Take him to your veterinarian tomorrow. If possible, collect a urine sample for analysis. This may be difficult if he's not using the litter box, so your vet will need to collect one with a needle and syringe (a cystocentesis). This will enable him to determine if there is an infection present, as well as whether there are crystals in the urine that may benefit from a diet change.
If your cat becomes painful in his abdomen, begins crying or licking excessively at his penis, if he is straining to urinate and nothing comes out, take him to an emergency clinic immediately.
Good luck, I hope he does well for you.