Schedule-induced polydipsia as a function of six water dipper sizes was examined in four food-deprived rats under Fixed Time 1- and 2-minute schedules. Increasing dipper size increased session water intake but did not affect the number of intervals containing at least one barpress (i.e., number of bouts), nor the number of barpresses per bout, nor the temporal distribution of barpressing within the interfood interval. Previous research showing polydipsic intake to be impervious to other types of restrictions on water availability have suggested the notion of a volume constancy mechanism. The present research raises questions about the operation of the volume constancy mechanism, questions about how to conceptualize the dipper size manipulation, and questions about variables which affect the temporal locus of drinking.