Abbie,
If the water level drops on the average 175 everyday for 6 days in a week, we could conclude that people drink 175x6 ounces weekly. So for 4 weeks straight, people would drink 175x6x4=4200 ounces
Since your water dispenser only holds 800 ounces, we would have to divide the 4200 ounces by 800 ounces to discover the number of refills that you would make within the 4-week span. This gives 4200/800= 5.25
This could be rounded off as 6 rounds really because you can't refill .25 of the time.
I hope this helps