 Why does Evans give up his drinking water?
Like when there's no use trying—when it's time to give up because it's hopeless.... The light from the star that died when the meteor was created fell on Earth before the first lungfish ventured from the sea. The shaft tried to tie itself into a knot, and the blades, damaged and undamaged were spit through the casing. It was two days to sunrise, where Evans stood. The shadow line between day and night could be seen from the Moon to be drifting across Australia. Evans, who had no watch, thought of the time as a quarter after Australia. Evans was a prospector, and like all prospectors, a sort of jackknife geologist, selenologist, rather. Once he followed a stampede to Yellow Crater, where he thought for a while that he had a fortune in chromium. The chromite petered out in a month and a half, and he was lucky to break even. Evans was about three hundred miles east of Williamson Town, the site of the first landing on the Moon. Evans was due back at Williamson Town at about sunset, that is, in about sixteen days. His drinking water—kept separate from the water in the reactor—might conceivably last just as long. But his oxygen was too carefully measured; there was a four-day reserve. Four days reserve—plus one is five—plus sixteen days normal supply equals twenty-one days to live. By the light of this, he reinspected the steam system, and found about three gallons of water frozen in the condenser. The condenser, like all condensers, was a device to convert steam into water, so that it could be reused in the boiler. This boiling lowered the temperature, and the condenser demonstrated its efficiency by quickly freezing the water in the tank. Evans sealed the turbine from the rest of the steam system by closing the shut-off valves. If there was any water in the boiler, it would operate the engine that drove the generator. Then, if the pump wasn't blocked by ice, it would return the water to the boiler. Carefully he poured a cup of his drinking water into a pipe that led to the boiler, and resealed the pipe. The water that he had poured into the boiler quickly turned into steam, and the steam turned the generator briefly. It was one day's supply if used wastefully. This was to allow the air-conditioning system to function properly, and to prevent air loss in case of the highly improbable meteor damage.
 Using the water is the only way for his transportation to work
 Using the water is the only way for his transportation to work  He knows he will be able to find more soon in one of the caves  He knows his rescuers will come find him and bring water  He knows he does not have enough to survive so he uses it to save his equipment