Water Catchment Capacity

The capacity of a rainwater harvesting system depends on the amount of rainfall, size of collection area, storage capacity, and the level of a household's demand for water.

Table 1.0 indicates the gallons of water produced annually for different size roof areas and rainfall amounts.
To determine the square footage of catchment area of a house, use only the house’s footprint. (The actual area of roof material will be greater due to the roof slope. However, the amount of rainfall on the roof is not affected by the slope.)

In Table 1.0, note that Austin’s average rainfall is 32 inches.

Table 1.0
Annual Rainfall Yield in Gallons for Various Roof Sizes and Rainfall Amounts

ROOF SIZE          RAINFALL IN INCHES
in Sq Ft.;

                       20       24       28        32      36       40       44       48        52

1000           11236 13483 15730 17978 20225 22472 24719 26966 29214

1100           12360 14832 17303 19775 22247 24719 27191 29663 32135

1200           13483 16180 18876 21573 24270 26966 29663 32360 35056

1300           14607 17528 20450 23371 26292 29214 32135 35056 37978

1400           15730 18876 22023 25169 28315 31461 34607 37753 40899

1500           16854 20225 23596 26966 30337 33708 37079 40450 43820

1600           17978 21573 25169 28764 32360 35955 39551 43146 46742

1700           19101 22921 26742 30562 34382 38202 42023 45843 49663

1800           20225 24270 28315 32360 36405 40450 44495 48540 52584

1900           21348 25618 29888 34157 38427 42697 46966 51236 55506

2000           22472 26966 31461 35955 40450 44944 49438 53933 58427

2100           23596 28315 33034 37753 42472 47191 51910 56629 61349

2200           24719 29663 34607 39551 44495 49438 54382 59326 64270

2300           25843 31011 36180 41348 46517 51686 56854 62023 67191

2400           26966 32360 37753 43146 48540 53933 59326 64719 70113

2500           28090 33708 39326 44944 50562 56180 61798 67416 73034