Utility of Rain Barrels for Irrigating Home Gardens

Typically 50 gallon drum used as storage cistern

Summer evapotranspiration (ET) (loss of water from soil surface through leaves) is .25 inches/day, if sunny day.

Water holding capacity of loam soils is 2 inches of water/foot of soil.

Effective rooting depth of many garden plants = 1 foot

From a plant management perspective, irrigation is best if no more than 50% of water holding capacity is depleted. For loam soil irrigate when 1 inch of ET.

So in summer, if irrigating for plant management (not drought management), irrigate every 4-5 days, adding one inch of water.

1 inch of water = .62 gallons over 1 square foot

50 gallons/.62 = 80.6 square feet of garden rooting area until cistern is refilled.