Space Exploration Stack Exchange is a question and answer site for spacecraft operators, scientists, engineers, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
An NIH abstract writes to say
A daily water intake of 3.7 L for adult men and 2.7 L for adult women meets the needs of the vast majority of persons.
Depends how you look at it. Onboard the International Space Station (ISS), water is definitely a precious resource and several measures were taken to consume less of it, such as recycling as much of it as possible, not washing clothes, reducing tap pressure, conserving it under shower and using wet cloths, using liquid waste vacuum tube on toilets, and so on. But it is also a consumable, since it's a source of oxygen through electrolysis and inefficiencies of the ISS' life support recycling used water further reduces its quantity, so it is supplied to the ISS regularly with resupply vehicles.
ISS astronauts aren't deprived of it though, and it's part of their daily regime to hydrate frequently to reduce effects of blood volume loss due to microgravity. I can't say that was the case with all manned missions to space though, for example, if Chinese taikonauts had sufficient water supply during their stay at Tiangong 2. And some earlier US manned missions only took really limited, one day's worth of water supplies with them, since they were short-duration flights only, such as the early project Mercury flights. And for Apollo missions, water was used to rehydrate the food and as onboard equipment coolant, on top of using it for drinking, so that was a bit of a problem during Apollo 13 mission, but they managed to make supplies they had left after the cryogenic tank stir explosion last by restricting its use.
To my knowledge, no astronaut yet suffered long term water shortage in space, with a slight exception of Apollo 13 crew but they made due. Recycling and conserving use is however essential to keeping supplies last even in Low-Earth Orbit (LEO) with resupply vehicles standing by and relatively easy escape route in case something goes badly wrong.
Sources and suggested reading:
