It's not.

Its color can vary from clear to nearly black, depending on what's wrong with you. It's yellow when you're dehydrated and it's concentrated; it can be red or pinkish from blood or nearly black from bile. It can taste sweetish in cases of diabetes (or so I'm told) and can contain "gravel" from bladder or kidney stones if you look at it under a microscope.

Which brings to mind a couple of lab techs I knew. Call them John and Mary.

They were working late one night back in the days before computers did all the work. Around 2 a.m. it was slow and they were catching up on the routine bloods and urines that had come in during the day. John was working on one that was so dark you couldn't see through it.

He did the pH, the specific gravity, and then put it under a microscope. It was FULL of what appeared to be sand. The patient was obviously very, very ill but John couldn't figure out from what. So he called Mary for a consult.

Mary looked long through the microscope and then picked up the specimen contain, sniffed it, and drank some.

Coffee. So playing along, they wrote up a report that the patient was suffering from acute arsenical poisoning.

Some days later John was drawing bloods up on the floor and impishly asked for a cup of coffee. The nurses at the station hurried to assure him that the coffee machine was broken.