Effects of effort and social modeling on drinking in humans

The role of economic and social influences on water intake in humans was explored in two experiments. In the first experiment, the effect of water cost (as defined as the amount of effort required to acquire water) on prandial drinking was studied by manipulating water position during an ad libitum meal: water was available either on the dining table, about 20 feet from the table, or approximately 40 feet away. Subjects drank significantly more when the water was on the table than in the other conditions; but a linear relationship between cost (distance) and intake was not observed. In the second experiment, the effects of water cost and a social model on drinking were assessed in a similar paradigm. Increasing effort required to obtain water significantly reduced prandial water intake, and the presence of a social model increased water intake. Although some interesting trends emerged, no significant interactions between social and economic factors were found. These experiments demonstrate that environmental factors can significantly affect facultative drinking in humans.