Piss tank data
There is a Bluesky bot which uses data from the International Space Station to provide updates on what % full the ISS's piss tank is.
This means that you can tell when people on the ISS have recently pissed - the percentage between two posts will jump up.
The Q+A thread says:
Q: And every time an astronaut up there pisses, the number goes up? Kind of. There's some buffer so the piss level rising doesn't correlate with an astronaut pissing. More on that further below.
You can also tell when the amount of piss in the tank is going down because they're recycling it into water. The piss percentage will slowly reduce, 1% at a time, over the course of hours.
Again, from the Q+A thread:
Q: Why do they even need a tank if they're recycling it? The recycler doesn't run 24/7, nor does it run quick enough that it instantly transform urine as it comes in.
So yes, the ISS recovers water from astronaut urine. I remember learning about this as a child but in the years since, I've forgotten most of what I knew about it. So I read that Q+A thread (highly recommend this) and also did a quick search and found some stuff.
Here is a research paper from 2020 about inefficiencies that existed at the time within the ISS piss treatment process. The abstract is great.
However, despite over 50 years of research and advancements on water extraction from human urine, the Urine Processing Assembly (UPA) and the Water Processor Assembly (WPA) now operating on the ISS still achieve suboptimal water recovery rates and require periodic consumables resupply. Additionally, urine brine from the treatment is collected for disposal and not yet reused. These factors, combined with the need for a life support system capable of tolerating even dormant periods of up to one year, make the research in this field ever more critical.
And here is a 2023 NASA press release about processing that brine, which is I guess a new technology installed since the 2020 paper I linked above to deal with the exact problem it focused on.
The BPA takes the brine produced by the UPA and runs it through a special membrane technology, then blows warm, dry air over the brine to evaporate the water. That process creates humid air, which, just like crew breath and perspiration, is collected by the station’s water collection systems.
Brine processing ups the water reclamation percent to 98%!
The bot doesn't say who made it, but I salute them. They do reference "other ISS piss tracking initiatives" in the Q+A thread... so I went looking and found a macOS menu bar that tracks piss and also works on iOS and Apple watches. Nice! There's also a website that shows the status of a variety of several water and waste related storage systems on the ISS.
It was fun to look up all this stuff. As a kid, astronaut data was highly interesting to me, and I used to know quite a lot about the waste management systems. It's crazy how much I've forgotten over the last 25 years...