When rain falls in the wrong season: storing winter rain for a summer garden

Timing matters more than the total

The total matters less than when it falls. What decides tank size is the share of rain that falls in the growing season, April to October. In 498 of 3,206 cities less than 40% does, and 388 of those need a cistern of 1,000 gallons or more. They are in Arizona, California, Idaho, Nevada, Oregon, Utah, Washington.

City	Rain (in/yr)	Falls Apr-Oct	Worth buying
Los Angeles, CA	14.1	12%	2,500 gal
San Diego, CA	11.0	17%	2,500 gal
San Jose, CA	18.8	18%	2,500 gal
San Francisco, CA	30.0	20%	1,500 gal
Seattle, WA	38.5	36%	165 gal
Portland, OR	44.9	34%	275 gal
Fresno, CA	11.4	20%	2,500 gal
Sacramento, CA	20.4	18%	2,500 gal

Summer-rain climates are the opposite

In 2,105 cities, including most of the country's largest, 60% or more of the rain falls April to October. Storms arrive while the garden is growing and refill a barrel within days, so 2,049 of them (97%) need nothing bigger than one or two barrels.

City	Rain (in/yr)	Falls Apr-Oct	Worth buying
New York, NY	47.1	62%	55 gal
Chicago, IL	34.4	74%	55 gal
Houston, TX	55.4	66%	55 gal
Philadelphia, PA	50.7	62%	55 gal
San Antonio, TX	34.0	67%	55 gal
Dallas, TX	41.4	61%	110 gal

What to do if you live in a winter-rain city

Decide whether you want to store for the summer or just use rain while it falls. A barrel or two still waters winter vegetables, fruit trees and spring planting, and costs little. Carrying water into July means storage sized from your city's tank table, a covered tank that keeps mosquitoes and light out for months, and a plan for the overflow in a big winter storm. Seeing the monthly pattern on your city's page is the quickest way to tell which kind of climate you have.