During many years, I peed in the sink of our old internal garage (which we used as a storage room). I did it only on evenings, when my daughter and girlfriend had already gone to bed.
The motive of my actions was totally altruistic: if I would use the toilet in the hall, I might wake them up and I didn’t want this to happen.
I made the crucial mistake though that I did not use enough water to flush the urine down the drain, and only near the end of my urinary adventure did I find out what the consequences of my altruism were. In one word: residue.
Tiny (and almost invisible) stone-like particles in my urine had accumulated over the years to form a stinky (and sandy) mass, which apparently was the perfect breeding grounding for the wrong kind of bacteria to amass (hence the stench). The mass also clogged the drain, and un-clogging it was confrontational for more than one reason. Anyways.
If I had used much more water though, there would not have been a problem whatsoever.
Urine (of a healthy person) is essentially sterile (although brief contact with genitals can soil it a little), and flushing it with gallons of water dilutes it so much that there are no health issues at stake. The controversy surrounding peeing in the shower is therefore totally psychological —
Nobody has ever died from an overdose of homeopathic medicine, after all.