Here's how the researchers came to this conclusion: At the beginning of the study, all the women emptied their bladders and gave a urine sample, then underwent an ultrasound to confirm that their bladders were totally empty. Then they stayed in the exam room either alone or with a partner and did something to get sexually aroused — but they didn't orgasm. Once the participants were sufficiently turned on, they invited the researchers back into the room for another ultrasound, where the researchers saw that the ladies' bladders had filled back up a little bit (which makes sense — some time had gone by). Then the researchers left the room again, and the women continued going at it until they squirted.
After the women squirted, they were given another ultrasound and found that their bladders were empty again. Seriously. There was urine in there before they squirted, and it was gone after they squirted. You see where we’re going with this?
The researchers also analyzed the liquid in the lab and found that it had the same chemical composition as urine, lead study author Dr. Samuel Salama, tells BuzzFeed Life. This fluid comes from the bladder and the chemical analysis shows that it originates in the kidneys, explains Salama. So, yeah... looks like it's diluted urine.