Daily food and water intake as well as water intake during 24-hr food deprivation were measured in 181 adult male rats of 15 inbred strains and 1 outbred stock. Strain differences in absolute and relative food intake were moderate but significant, whereas strain differences in absolute and relative water intake under both conditions were dramatic. During food deprivation some strains showed little depression of daily water intake, while other strains consumed less than 20% of their usual ad lib intake. Possible explanations, both genetic and environmental, for the divergent patterns of water intake during food deprivation are presented. In light of such strain differences, generalizations about the drinking behavior or water intake regulation of the rat must be made with caution.The interrelation between feeding and drinking under ad lib and various deprivation conditions has been demonstrated in a number of species (e.g., Bolles, 1961;Cizek, 1961;Fitzsimons & Le Magnen, 1969). In most animals the ingestion and digestion of food, particularly dry food, induces a major hydrational requirement to which body water regulatory systems must respond. Although reduced water intake during periods of food deprivation might be expected (as a homeostatic adjustment to decreased water need), food deprivation has in fact diverse effects on drinking behavior. During total or partial food deprivation, water intake typically has been observed to decrease in rats (e.g., Nims & Sutton, 1954;Verplanck & Hayes, 1953) and dogs (Kleitman, 1927) but to increase in hamsters and gerbils (Kutscher, 1969) and humans (Keys, Brozek, Henschel, Mickelson, & Taylor, 1950). Both increases and decreases have been reported for mice (Kutscher, 1974), rabbits (Cizek, 1961), and guinea pigs (Cizek, 1954;Kutscher, 1969). Although some research has focused on these interesting species
