Page 137 - WaterSense at Work

October 2012
Current Water Use
To estimate the current water use of an existing garbage disposal during idle periods,
identify the following information and use Equation 4-18:
Flow rate of water through the garbage disposal. This flow rate typically ranges
from 2.0 to 15.0 gpm.
Average daily idle period of the garbage disposal. Idle period is the time when
the garbage disposal is turned on but not in use. While this will vary by facility,
some estimates indicate that garbage disposals are typically used three hours
per day. For a facility operating 12 hours a day, this would mean an idle period of
nine hours if the garbage disposal is kept on throughout the day.
Days of facility operation per year.
Equation 4-18. Water Use of Garbage Disposal During Idle Periods (gallons per year)
= Flow Rate Through Garbage Disposal x Daily Idle Period x Days of
Facility Operation
Flow Rate Through Garbage Disposal (gallons per minute)
Daily Idle Period (minutes per day)
Days of Facility Operation (days per year)
Water Use After Retrofit
To estimate the water use from an existing garbage disposal that is retrofitted with a
load sensor during idle period, use Equation 4-18, substituting the reduced idle flow
rate. A load sensor can reduce the idle flow rate when the garbage disposal is not in
use to as little as 1.0 gpm.
Water Savings
To calculate the water savings that can be achieved from retrofitting an existing con-
ventional garbage disposal, identify the following and use Equation 4-19:
Current water use as calculated using Equation 4-18.
Water use after retrofit as calculated using Equation 4-18.
Food Disposals