Here's the Scoop On Cat Pee

     Humans, most anyway, are repulsed by urine, but for animals it's different. Cats, for example, communicate with their pee. They mark their territories with it and males announce they're available for mating and to warn other tomcats to back off. 
     Urine starts with water which regulates body temperature, carries nutrients and oxygen to the body’s cells and flushes out waste. 
     Cats in the wild get much of their fluids from prey, but for domestic cats who are fed dry food, it's only about about 10 percent water, so cats need to drink a lot of water. Canned food is around 80 percent water, so cats who eat this type of diet will likely drink a lot less water, because they’re getting it in their food. Our cat supplements her need for water by drinking out of the toilet. 
     Drinking water doesn’t directly produce urine; water mammals drink goes through the digestive tract and is absorbed into the bloodstream, then the kidneys filter the blood. 
     Cat urine contains about 95 percent water and 2 percent urea, a waste product resulting from protein metabolism. It's advised that cats should be taken to the vet if you notice that its urine is any other color than amber/yellow and perhaps because it's concentrated, a little on the dark side. Who checks their cat's pee? Although I suppose you'd notice it when scooping their litter box. 
     A urinary blockage or ruptured bladder can cause urine flow to stop. If a cat produces too little urine in a 24-hour period, it could indicate dehydration, kidney failure or a urinary blockage. If a cat produces too much urine, diabetes or other illness might be the cause. 
     Cat urine has a unique order because of the high levels of protein in their meat diet. It contains an amino acid called felinine. Although felinine is odorless to humans, it breaks down into stinking sulfur-containing compounds that produce pungent odors. Males cats that aren't neutered produce about three times more stink producing chemicals than neutered males or females, because they have more testosterone. 

     The odors serve as territory markers and attract females. If a cat pees on your carpet or furniture, the odor is difficult to remove. Cats have a superior sense of smell, so they will be able to pick up on the pheromones left behind even if we humans can't detect it. And, the sulfur-containing compounds are not eliminated by regular cleaners. You have to use cleaners with certain enzymes that break down cat urine compounds, even those only detectable to the cat or else they will continue to mark the spot. 
     The Cornell Feline Health Center reports that more than 30 percent of cats will get kidney disease in their lifetime. Older cats, half over the age of 15, have a form of kidney disease. Chronic kidney disease has no cure, but veterinarians today can detect the chronic form early and slow its progression allowing the cat to live a quality life with proper diet and treatment. 
     Just like humans, cats like a clean bathroom so if they’re peeing outside the box, something is wrong. If a cat takes a whiz outside the box it might have health issues, they might be upset about something that changed in their environment or maybe the condition of their litter box displeases them. 

Some possible causes: 
1) Pee on vertical surfaces – there are other cats are around and your cat is communicating with them. 
2) Nervous pee - usually happens when the cat becomes anxious and can’t make it to the litter box. It's usually on horizontal surfaces. 
3) Normal peeing - they have a clean litter box and a home they perceive as safe. 

Here is an interesting article on the effects of breathing cat urine.