PHOENIX — With their packs full, their canteens overflowing and their reserve bottles filled to the brim, outdoorsy Arizonans set out on foot this time of year under the scorching sun. But as they navigate the state’s picturesque trails, they face not only physical challenges but ethical ones, like how much water to share with strangers who have miles to go and not a drop to drink.

The question comes up on South Mountain, an urban refuge in southern Phoenix, on the four-mile hike down into Fossil Springs a couple of hours north and, most definitely, along the steep pathways that descend into the Grand Canyon. Wherever it is, hikers regularly encounter strangers gasping trailside from the heat.

“If it came down to having enough for myself or helping someone, I’d have to drink my own water,” said Laura Craig, a Phoenix businesswoman who shared some of her extra water with distressed strangers on a recent hike at Fossil Springs. “It’s an ethical decision. You hate to think of things like survival of the fittest, but it does come down to that.”

A hiker who had run out of water died in the Grand Canyon last weekend after some backpackers he had encountered, who were parched themselves, shared some of their water with him.