your math is WAY off man
8hrs*60min = 480 - 20min on filling = 460 / 60 = 7.666 hrs * 5.15/hr = $39.483 EARNED
8hrs*5.15/hr = $41.20 EARNED if he isn’t filling bottles and wasting time
41.20-39.49 = $1.71/day lost
and ok sure $2.50 for a few bottles of water
2.50 saved - 1.71 lost = $0.79 gained

this is far from the $7.50 a day you are trying to claim

now here is the real kicker, the company pays no matter what, they aren’t docking people for filling water bottles or cups with water, or taking pee breaks or anything else. so he’s actually saving time that he would be working, to do something much less important, and i’d assume easier than his job. sounds like a great deal to me