Post Falls, ID rainwater: 20,156 gallons off a roof

How much rain a roof in Post Falls, ID collects

20,156gallons a year

That is a 1,500 sq ft asphalt roof under Post Falls, ID's normal 25.4 inches of rain, about 795 gallons for every inch that falls.

Post Falls, ID has gaps between storms long enough to drain a single barrel. Around 165 gallons of storage catches most of what is worth catching.

Rainfall: NOAA 1991-2020 climate normals, the Coeur D'Alene station (7.5 mi away). Post Falls, ID ranks 4th wettest of the 26 cities covered in Idaho.

Month by month in Post Falls

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	3.21	2,551
Feb	2.11	1,677
Mar	2.68	2,130
Apr	1.91	1,518	304
May	2.14	1,701	276
Jun	2.17	1,725	272
Jul	0.73	580	451
Aug	0.77	612	446
Sep	0.81	644	441
Oct	2.02	1,606	290
Nov	3.34	2,655
Dec	3.47	2,758

Dec is the wettest month (3.47 in, 2,758 gal off the roof); Jul the driest (0.73 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.

Barrel or cistern in Post Falls?

Best fit: 3 linked 55-gallon barrels, which delivers about 1,985 gallons to the garden in a normal year (80.0% of its need).

If you buy one, link barrels with a short hose at the base so they fill and drain together, and check the overflow points away from the house.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	1,302	17,684
110 gal	1,710	17,277
165 gal	1,985	17,002
275 gal	2,136	16,850
550 gal	2,136	16,850
1,000 gal	2,136	16,850
1,500 gal	2,136	16,850
2,500 gal	2,136	16,850
5,000 gal	2,136	16,850

Simulated storm by storm through a normal year using the station's count of days with 0.1 in or more of rain each month.

Is rainwater collection legal in Idaho?

Allowed through a legal clarification made by the Office of the Attorney General

From the 2015 (Pacific Northwest National Laboratory report 24347); not yet re-checked against current law, so check with your state water agency before building anything large. Source