Water Usage vs FTE Classification

Hi, We are working on sizing a rainwater tank for a new building on an urban high school campus. There are several buildings on this campus and we are questioning the water usage calculations that LEED assumes based on the FTE. With the students entered as students (not transients), they trigger the same flush water demand as FTE’s which results in much more flush water use and a much larger tank than originally anticipated. LEED for Schools appears to approach “Students” as though they’re occupants of the building for the whole day, which is not really representative of the our school's model with multiple buildings and restrooms available throughout the day. Has anyone had this situation or were you able to use an alternative compliance approach to argue that the occupancy be reclassified?