Tank size by roof
Coastal San Diego: about 10 inches a year
Roof area is the footprint seen from above, not the slope. The catch assumes about 85 percent of the rain reaches the tank. A starter tank holds about two one-inch storms.
| Tank to start from | Rain caught in a year, at 10 in | |
|---|---|---|
| 1,000 sq ft of roof | Tank to start from1,000 gal | Rain caught in a year, at 10 inAbout 5,300 gal |
| 1,500 sq ft of roof | Tank to start from1,500 gal | Rain caught in a year, at 10 inAbout 7,900 gal |
| 2,000 sq ft of roof | Tank to start from2,000 gal | Rain caught in a year, at 10 inAbout 10,600 gal |
| 2,500 sq ft of roof | Tank to start from2,500 gal | Rain caught in a year, at 10 inAbout 13,200 gal |
| 3,000 sq ft of roof | Tank to start from3,000 gal | Rain caught in a year, at 10 inAbout 15,900 gal |
Inland numbers
Inland and foothills: about 14 inches a year
Rain climbs as you move inland and uphill. The last column is what a single one-inch storm adds, which is the same wherever you live.
| One 1-inch storm adds | Rain caught in a year, at 14 in | |
|---|---|---|
| 1,000 sq ft of roof | One 1-inch storm addsAbout 530 gal | Rain caught in a year, at 14 inAbout 7,400 gal |
| 1,500 sq ft of roof | One 1-inch storm addsAbout 790 gal | Rain caught in a year, at 14 inAbout 11,100 gal |
| 2,000 sq ft of roof | One 1-inch storm addsAbout 1,060 gal | Rain caught in a year, at 14 inAbout 14,800 gal |
| 2,500 sq ft of roof | One 1-inch storm addsAbout 1,320 gal | Rain caught in a year, at 14 inAbout 18,500 gal |
| 3,000 sq ft of roof | One 1-inch storm addsAbout 1,590 gal | Rain caught in a year, at 14 inAbout 22,200 gal |
The arithmetic
Three numbers behind every row
0.62
gallons per square footfor each inch of rain on a roof's footprint
85%
reaches the tankafter splash, overflow and the first flush, as a working figure
2
storms fill a starter tankof one inch each, a rule of thumb for first sizing
Rounded. Rainfall comes from NOAA's 30-year averages and varies by address, roof material and pitch. We measure your roof before we quote a tank.
What a tank can do
A tank is a buffer, not a summer supply
Most of the year's rain falls between November and March. A tank holds a few storms' worth and a drip line spends it over the weeks after. In a dry year it stays low, so we plan the garden to cope: mulch basins, low-water plants and drip zones matched to what the tank holds.
Mulch basins stretch every gallon
Drip zones sized to the tank
No promise of a bill drop: water rates and rainfall both change
The permit note
What needs a permit, and what we do about it
Rules differ by city and county and they change. This is how it usually goes in San Diego County; your building department decides.
Washer to landscape
California lets a simple clothes-washer system go in without a permit when it meets the state's listed conditions, such as mulch basins and no surface pooling. We build to those conditions.
Other greywater
Showers and bathroom sinks take a permit and a plan. We draw it and file it.
Rain tanks
Small above-ground tanks often need none. Large, buried or house-plumbed tanks usually do. We say which at the visit.
Who files, who pays
Dulce Godinez files for you. The city's fee is yours and is listed outside our estimate.
Send us the roof
Tell us the town and the rough size, and we'll check the table against your roof.