Sex is inherently wet, wet in all its aspects.
Arousal means oozing, slippery vaginal juices, shiny drops of precum, saliva on lips and tongue.
Some people like their sex to be more than a little wet. Watersports aficionados sometimes prefer their favorite wetness, piss, to be measurable in quarts, not drops. Besides volume, urine fetishists may admire its taste, color, and odor. It feels nice coming out, and those who enjoy drinking it think it feels nice going in, too. Some piss players enjoy marking or being marked with this product of the body, a sign of possession, dominance, or submission.