I’ve seen similar methods of the piss one before but with variations. They all essentially just revolve around taking impure water such as seawater (or piss i guess) and then letting it evaporate in a way that the recondensed droplets can be collected.
The method I read about (in a YA survival novel when I was like 12) involved taking a pot of water, building a tent shaped dome over it with a plastic tarp or something, setting some containers near the corners of the ‘tent’ and then boiling the water. When that happens the steam will hit the inside of the tarp and condense into water droplets which will roll down the raised corners of the tarp into the containers below.
It’s pretty labor/time intensive but the combo of boiling and condensation means the water should be very safe to drink, provided your tarp is clean.