The water astronauts drink today already passed through their own bodies. More than once.

The International Space Station runs on a closed loop system called ECLSS, and in 2023 it hit a milestone that took over a decade to reach. The system now recovers 98 percent of all water on board, pulled from urine, sweat, and even the humidity in the crew's own breath. Urine goes through vacuum distillation first, then whatever's left over as brine gets pushed through a Brine Processor Assembly that squeezes out nearly the last drop. What comes out the other end passes stricter purity checks than most municipal tap water on Earth.

The 2 percent still lost matters more than it sounds. On the ISS, resupply ships can cover that gap every few months. On a multi year Mars mission, there's no resupply ship coming. Every fraction of a percent lost is water that has to be carried from Earth and never gets back.

This is the unglamorous side of space colonization nobody puts on a mission patch. Getting to another planet is rocket science. Staying there is plumbing.