How do astronauts pee?

In microgravity, liquid doesn't fall: it forms drops that stick to walls or drift through the cabin. The whole architecture of space toilets stems from this fact. The main piece of equipment is a flexible funnel, a separate one for each crew member, extended by a hose and connected to a fan. As soon as the valve opens, a constant airflow sucks up the urine and carries it toward the tank, without a single drop escaping. The same principle, with a stronger airflow and a collection bag, applies to solid waste.

Men and women use the same device: the funnel's shape allows it to be used standing or sitting, and it is cleaned and stowed after each use. The equipment installed on board since 2020, the Universal Waste Management System, was specifically redesigned for more comfortable use by women, with a reworked seat and funnel.

Aboard the International Space Station, urine doesn't disappear into a lost tank. It goes into the Environmental Control and Life Support System, which distills it, then processes the condensate along with cabin humidity and crew perspiration. NASA states that the whole system recovers about 98% of the water astronauts bring on board, a threshold reached in 2023 thanks to an additional brine-processing system. The resulting water is purer than much of the tap water on Earth, and the crew drinks it.

In a spacesuit, during a spacewalk or during launch and reentry phases, no plumbing is available: astronauts wear a disposable absorbent undergarment, the Maximum Absorbency Garment. The first American flights improvised with a simple condom connected to a bag, a notoriously unreliable solution that later missions quickly abandoned.