That's not the only reason to think the space water would be unpalatable. Mineral specimens collected by the Mars rovers (on other parts of the planet) have turned up significant quantities of jarosite, a salt deposit that tends to form only in very acidic solutions. Researchers guess that the jarosite precipitated from a liquid with a pH of between 0 and 4. For comparison, a human can handle an acidic beverage like Coca-Cola, which has a pH of about 2.4, but more concentrated acids will cause mucosal injuries to the esophagus, stomach, and intestines. (Anything with a pH of less than 5.5 can affect the surface of your teeth.)
(Read more on why it might not be a good idea to drink the water on Mars.)
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