Reserved for the return

Original non-fiction-style practice text.

The cycling group reached the hilltop shelter with water left in every bottle. A few riders poured some over their heads. Their leader, Safiya, asked them to stop. She had allowed for a refill at the shelter, but a notice on the locked tap said its supply was unavailable.

The outward ride had been cool and mostly downhill. The route back would take them uphill during the warmest part of the day. Safiya divided the unopened spare bottles between the riders and chose a shorter return. One participant said the group was being overcautious because nobody felt thirsty yet.

Safiya replied that their present comfort did not describe the journey still ahead. She was not counting the water they had needed to reach the shelter. She was considering the water available for getting home under different conditions. They returned by the shorter lane, arriving while the village shop was still open. Several riders bought drinks before discussing the hilltop view.

Explain why Safiya thinks the riders’ lack of thirst is a poor reason to use up their remaining water.