Passage
Over a hot, dry summer, the water level in a small pond fell by nearly a third. No stream or pipe carried water out of the pond over its surface, and no one removed water from it. Two students agreed that the level had dropped but disagreed about where the missing water had gone.
Student 1: The water was lost mainly by evaporation from the pond's surface. Heat from the sun and dry air turn surface water into vapor, which drifts away into the air. On this view, the level should fall fastest on hot, dry, windy days and change very little on cool, humid, still days. A wide, shallow pond should also lose level faster than a narrow, deep pond holding the same amount of water, because a wider surface exposes more water to the air.
Student 2: The water was lost mainly by seepage downward through the pond's bottom. Water slowly soaks through the soil at the bottom and joins the groundwater below. On this view, the level should fall at a fairly steady rate whatever the weather, and a pond with a sandy, porous bottom should drop much faster than one lined with packed clay, even during cool, cloudy weather.
