The following article taken from QX Magazine issue 685:

Dear Dr Vass,
What are the dangers of drinking urine or letting a
guy urinate on me or in my ass? I went to club recently
and guys were just waiting around in the urinals to be
pissed on. Surely this isn’t very healthy!?
Sam, 32

Alex Vass says,
Hi Sam,
Guys who are into watersports get sexual kicks from being urinated on or from urinating on others. Some like to drink urine. And most likely there are many other permutations!
But what about the health risks? Urine is usually sterile and made up if water and excess body wastes like nitrogen, potassium and urine or you let a guy urinate inside you, your body will absorb these chemicals through the stomach or through the lining of the colon. But if you have medial problems like high blood pressure, diabetes or kidney problem you may make your condition worse because you will be forcing your kidneys to work extra wastes from your body.
And more importantly urine is not always sterile and can contain bugs. For example, if your partner has a sexually transmitted infection affecting his penis like gonorrhoea, syphilis or chlamydia then these will be washed out and transferred into your throat or arse. HIV is thought to possibly be present in urine. However, it’s not thought to a risk. But his dick should not be there without a condom in the you, anal sex could easily follow and this would then put you at great risk of picking up HIV if he was positive.
Urine can also contain caustic substances that can easily irritate and then to pick up sexually transmitted infections from urine. And if diarrhoea because it’s similar to getting an enema.
If you are going to get into watersports the safest way is to keep your enjoyment to golden showers (urinating on someone’s skin). As long as you don’t get urine on unbroken skin, in your eyes, mouth or arse then there is probably no health risk.

http://www.qxmagazine.com/pdf/backissues/qx685.pdf