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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.

Mars One touts a crew-size of four with a proposed transit duration of 210 Earth days. Assuming four males, the minimum figure works out to 3108 litres with the caveat nobody consume more than their 3.7 litres daily.

The brief on MTV (Mars Transit Vehicle) writes to say

The Transit habitat has a mass of about 20,000 kg. It will carry close to 800 kg of dry food, 3000 liters of water and 700 kg of oxygen on board. No water or Oxygen will be recycled, because the trip lasts only 210 days.

Even assuming 3000 litres is merely for the purpose of consumption, the short-fall is 108 litres. In other words, one crew member may have to forgo water for a month (a little in excess of 29 days). The short-fall increases still further if this 3000 litres also provides for cooking, and other mundane activities.

Will the Mars Transit Vehicle need to include a water recycling system?

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    $\begingroup$ They should probably pack a little hydrogen & use the Sabatier hardware to scrub CO2. Hamilton quotes 227 gal (859 liters)/year, 4 crew vs. 6 reduces that to 573 l/yr, or 329 liters for 210 days. $\endgroup$ – Jerard Puckett Feb 17 '14 at 3:43
  • $\begingroup$ Maybe the answer is to just not have a purely male crew? $\endgroup$ – PearsonArtPhoto Feb 17 '14 at 14:03
  • $\begingroup$ @PearsonArtPhoto The thought crossed my mind. If crewed entirely by females the figure works out to 2268 litres for consumption; a far more comfortable figure. But add even 0.5 litre per person for, say, mundane activities (rehydrating food, daily stuff, washing) - and it gets dicey again. Their margins should be better. $\endgroup$ – Everyone Feb 17 '14 at 14:09
  • $\begingroup$ Rehydrating food is still taking in water (You don't have to drink it if it's in the water). Washing is the real key... $\endgroup$ – PearsonArtPhoto Feb 17 '14 at 14:11
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They need one, but they don't admit it...

In general, most long term space habitats are expected to engage in water recycling. NASA has always done so.

They Claim

The Mars One site, however, indicates that they will not be recylcing.

In their own words:

It will carry close to 800 kg of dry food, 3000 liters of water and 700 kg of oxygen on board. No water or Oxygen will be recycled, because the trip lasts only 210 days. Not recycling these components eliminates the need for recycling systems, backups, spare components and reduces power and cooling requirements. The 3000 liters of water is also used for radiation shielding. - See more at: http://www.mars-one.com/technology/mars-transit-vehicle#sthash.grUA54kZ.dpuf

Discussion

I expect that this is an unrealistic mission plan on their part, and, since they're based in the US, the Feds will require them to include some recycling gear, as 3.57L is not much. (I drink half that much on a typical day of reading. Sometimes, I drink more than that much in a day, especially if working.)

Further, since they plan on using that water as a radiation shield, they must either replenish it, or they will be exposing the crew to ever increasing levels of radiation.

Further, given the stored food, they're going to need to purge water from the atmosphere aboard, so concentration of water vapor in a dehumidification process can be a ready source for some additional water.

Also note: bathing in 0G can be done in under 2L, but typical on the ISS is close to 4L to bathe - but that bathing isn't a daily need, either, in 0G.

NASA notes in an educational page that up to about 10.6 Tons of water per year is needed per astronaut. That's 10,600L per year, or 30L per day.

So, the MarsOne 3000L for 4 people is unreasonable. It would be rationing the whole time, and require that the astronauts not be sweating. Humans can lose up to 2L per day just by respiration if the air is too dry, and need at least a liter per day for metabolic purposes, and up to another 2L can be sweat out if engaged in high activity or exposed to high heat.


http://www.mars-one.com/technology/mars-transit-vehicle
http://www.mars-one.com/faq/health-and-ethics/how-much-living-space-will-the-astronauts-have

http://science1.nasa.gov/science-news/science-at-nasa/2000/ast02nov_1/

http://www.nasa.gov/audience/foreducators/stseducation/materials/Sustaining_Life.html

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