How much graywater does a residential graywater system produce?
The formula to determine the estimated volume of graywater produced is:
GW = 15 * 7 * OF (use for a clothes washer graywater system)
GW = 40 * 7 * OF (use for a simple or complex graywater system collecting graywater from all available sources)
Where:
GW = estimated graywater produced (gallons per week)
OF = the number of occupants
Note: If the number of occupants is not known, the California Plumbing Code (CPC) assumes two occupants for the first bedroom and one additional occupant for each additional bedroom. 15 gallons per day and 40 gallons per day come from the CPC.
Please see Chapter 16A Part 1 of the 2010 California Plumbing Code for more information regarding the volume of graywater generated.
What landscape size can I use the graywater for?
The formula to estimated the amount of landscape area that can be irrigated using graywater is:
LA = GW / (ET * PF * 0.62)
Where:
LA = landscaped area (square feet)
GW = estimated graywater produced (gallons per week)
ET = evapotranspiration (inches per week), use 1 inch per week. The average for most parts of Los Angeles is 50.1 inches per year.
PF = plant factor (either 0.3, 0.5, or 0.8) based on climate and type of plant
0.62 = conversion factor (from inches of ET to gallons per week)
Please see the State Guide for Landscape Irrigation for more information regarding the ET and PF and for other landscape and irrigation requirements.
How much can I save on my LADWP utility bill?
As of July 2011, the LADWP first-tier water rate for single-dwelling unit residential customers is $3.437 per Hundred Cubic Feet (HCF). For a family of four that produces 1,120 gallons of graywater per week, this is equivalent to a potential savings of $267 in water costs per year.
Furthermore, a reduction in your water bill could lead to a reduction in your Sewer Service Charge (SSC) as well. Your SSC is calculated based on metered winter water usage when irrigation is at a minimum. So, if you reduce your metered water usage, you can reduce your SSC. Currently, the SSC is $3.27 per HCF.
HCF equates to 748 gallons
Water rates are adjusted quarterly. To view the current rate, please go to Residential Water Rate.