How Astronauts Sleep, Shower, and Use the Toilet Aboard the ISS in Microgravity

There is no up and no down on the International Space Station. When astronauts close their eyes, their bodies don't sink into a mattress, they hover wherever they happen to be, drifting slowly with every air current from the ventilation system. Left untethered through the night, a sleeping astronaut can drift into a wall, a piece of equipment, or a crewmate. So they sleep in small personal crew quarters, roughly the size of a phone booth, and zip themselves into sleeping bags anchored to the wall.

The bags hold the body in place, but the arms are the problem. In microgravity, a relaxed human body assumes what NASA calls the neutral body posture: knees slightly bent, arms floating forward at chest height, like a person perpetually bracing for a fall. Astronauts often wake to find their arms drifting in front of their faces. Some tuck their arms inside the sleeping bag. Some don't bother.

The ISS orbits Earth every 90 minutes, which means astronauts experience 16 sunrises and 16 sunsets every single day. Without intervention, this destroys circadian rhythms. The station's lighting system adjusts colour temperature across the day to simulate a normal cycle, and astronauts follow a strict schedule. Sleep quality in space is still a documented problem: a 2014 study published in The Lancet Neurology found that astronauts on long missions sleep an average of six hours per night despite being scheduled for eight, and many rely on sleep aids like zolpidem or melatonin.

Water in microgravity does not flow. It clings. A drop released from a tap forms a perfect sphere and floats until it hits a surface, a wall, a face, a piece of electronics. A shower in the conventional sense would fill the cabin with thousands of drifting water globules, and water near electrical systems is catastrophic. The ISS has no shower stall and no running water for bathing.

Instead, astronauts use rinseless shampoo and no-rinse body wash, the same products originally developed for hospital patients who cannot bathe conventionally. Water is dispensed from a bag through a nozzle in small controlled amounts. An astronaut squirts water onto a washcloth and wipes down. The washcloth itself must be wrung out carefully, because water squeezed from fabric forms those same floating spheres. Oral hygiene works the same way: astronauts use a toothbrush and toothpaste, but they swallow the toothpaste rather than spit it, or they spit into a towel. There is no sink to spit into.

Hair washing is a small production. Canadian astronaut Karen Nyberg posted a video from the ISS showing exactly how it's done: a pouch of warm water squeezed onto the scalp, rinseless shampoo worked in with fingers, then the water absorbed with a towel. The whole process takes about ten minutes and uses roughly 200 millilitres of water. On Earth, a standard shower uses anywhere from 40 to 80 litres.

This is the section everyone actually wants to read. The ISS toilet, officially the Waste Collection System, works on suction, not gravity. Where a ground toilet uses water to carry waste down and away, the space toilet uses airflow to pull waste in the correct direction. Astronauts position themselves carefully over the opening, which is about 10 centimetres in diameter, and a fan creates airflow that directs solid waste into a collection bag. The bag is sealed, compressed, and eventually loaded onto a cargo spacecraft that burns up on re-entry into Earth's atmosphere. The waste, in a sense, becomes a shooting star.

Urine is handled differently, and this is where the engineering gets genuinely remarkable. The ISS carries the Urine Processor Assembly, part of the Environmental Control and Life Support System. Urine is collected through a separate funnel-and-hose attachment, processed through a series of filtration and distillation stages, and converted into potable water. NASA estimates the system recovers about 93 percent of water from urine. Astronaut Sunita Williams, who has spent more than 300 days in space across two missions, described the recycled water as tasting cleaner than most tap water on Earth. The agency's own summary of the system puts it plainly: today's coffee becomes tomorrow's coffee.

Gaganyaan, India's first crewed spaceflight program being developed by ISRO, will require its own life support and waste management systems for the crew. The specific configurations have not been publicly detailed at the level of the ISS documentation, but the engineering challenge is identical: in microgravity, every bodily function that humans take for granted on the ground requires a purpose-built mechanical solution.

The ISS has been continuously inhabited since November 2000. Every solution described above was developed, tested, and refined across more than two decades of human presence in orbit. The rinseless shampoo, the vacuum toilet, the urine recycler, none of these existed in their current form before the station demanded them.

Water recycling is the clearest example of why this matters for missions beyond low Earth orbit. A crewed mission to Mars would take roughly seven months in transit each way, with no resupply possible. Every kilogram of water that must be launched from Earth costs approximately $22,000 in fuel alone, by NASA's historical estimates. A system that recovers 93 percent of water from waste and exhaled breath is not a curiosity, it is the difference between a Mars mission that is financially possible and one that is not.

The unglamorous details of sleep, hygiene, and sanitation turn out to be the load-bearing problems of long-duration spaceflight. Propulsion gets the spacecraft there. Life support keeps the crew alive long enough to arrive.