second off. The burn, at 79:27:38.95, lasted four minutes and 23 seconds. The crew then shut down most LM systems to conserve consumables. Return to Earth The LM carried enough oxygen, but that still left the problem of removing carbon dioxide, which was absorbed by canisters of lithium hydroxide pellets. The LM's stock of canisters, meant to accommodate two astronauts for 45 hours on the Moon, was not enough to support three astronauts for the return journey to Earth. The CM had enough canisters, but they were of a different shape and size to the LM's, hence unable to be used in the LM's equipment. Engineers on the ground devised a way to bridge the gap, using plastic, covers ripped from procedures manuals, duct tape, and other items. NASA engineers referred to the improvised device as "the mailbox". The procedure for building the device was read to the crew by CAPCOM Joseph Kerwin over the course of an hour, and it was built by Swigert and Haise; carbon dioxide levels began dropping immediately. Lovell later described this improvisation as "a fine example of cooperation between ground and space". The CSM's electricity came from fuel cells that produced water as a byproduct, but the LM was powered by silver-zinc batteries which did not, so both electrical power and water (needed for equipment cooling as well as drinking) would be critical. LM power consumption was reduced to the lowest level possible; Swigert was able to fill some drinking bags with water from the CM's water tap, but even assuming rationing of personal consumption, Haise initially calculated they would run out of water for cooling about five hours before reentry. This seemed acceptable because the systems of Apollo 11's LM, once jettisoned in lunar orbit, had continued to operate for seven to eight hours even with the water cut off. In the end, Apollo 13 returned to Earth with of water remaining. The crew's ration was 0.2 liters (6.8 fl oz) of water per person per day; the three astronauts lost a total of among them, and Haise developed a urinary tract infection. This infection was probably caused by the reduced water intake, but microgravity and effects of cosmic radiation might have impaired his immune system's reaction to the pathogen. Inside the darkened spacecraft, the temperature dropped as low as . Lovell considered having the crew don their spacesuits, but decided this would