Your Runoff in A Few Simple Steps!
The general rule of thumb is for 1,000 square feet of catchment surface, each inch of rain produces 600 gallons of harvestable water. With an average of 44 inches of rain per year in Marin County, that amounts to 26,400 gallons!
Said another way:
One inch of rain on a thousand square foot roof = Approximately 600 gallons!
44 inches of rain per year on a thousand square foot roof = Approximately 26,400 gallons!
Said another way:
One inch of rain on a thousand square foot roof = Approximately 600 gallons!
44 inches of rain per year on a thousand square foot roof = Approximately 26,400 gallons!
Definition: Catchment Area
Length (feet) x Width (feet) of a rectangular roof, driveway, parking lot or other impervious surface.
Download the Rainwater Harvesting Calculator
This is an Excel file adapted from Brad Lancaster's website.
| marin_catchment-area-to-runoff-yield-3.xls |
Annual Rainfall Averages - Marin County
(From 50-year average annual precipitation map located in the Marin Countywide Plan)
Belvedere
Bolinas
Corte Madera
Fairfax
Forest Knolls
Greenbrae
Kentfield
Lagunitas
Larkspur
Mill Valley
Bolinas
Corte Madera
Fairfax
Forest Knolls
Greenbrae
Kentfield
Lagunitas
Larkspur
Mill Valley
22"
26"
32"
40"
40"
32"
44"
44"
40"
32"
26"
32"
40"
40"
32"
44"
44"
40"
32"
Muir Beach
Novato
Point Reyes
Ross
San Anselmo
San Rafael
Sausalito
Stinson Beach
Tiburon
Woodacre
Novato
Point Reyes
Ross
San Anselmo
San Rafael
Sausalito
Stinson Beach
Tiburon
Woodacre
26"
26"
36"
44"
40"
28"
24"
30"
22"
44"
26"
36"
44"
40"
28"
24"
30"
22"
44"
