Portales, NM rainwater: 12,796 gallons off a roof
Rainwater from a roof in Portales, NM
12,796gallons a year
That is a 1,500 sq ft asphalt roof under Portales, NM's normal 16.1 inches of rain, about 795 gallons for every inch that falls.
In Portales, NM a single barrel does most of the work. Storms come often enough that a small tank refills before it runs dry, and a bigger one would mostly sit full.
Rainfall: NOAA 1991-2020 climate normals, the Portales station (0.3 mi away). Portales, NM ranks 3rd wettest of the 19 cities covered in New Mexico.
Month by month in Portales
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.50 | 397 | |
| Feb | 0.37 | 294 | |
| Mar | 0.74 | 588 | |
| Apr | 0.68 | 540 | 458 |
| May | 1.51 | 1,200 | 354 |
| Jun | 2.14 | 1,701 | 276 |
| Jul | 2.29 | 1,820 | 257 |
| Aug | 2.91 | 2,313 | 180 |
| Sep | 1.92 | 1,526 | 303 |
| Oct | 1.82 | 1,447 | 315 |
| Nov | 0.56 | 445 | |
| Dec | 0.66 | 525 |
Aug is the wettest month (2.91 in, 2,313 gal off the roof); Feb the driest (0.37 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 Portales?
Best fit: 2 linked 55-gallon barrels, which delivers about 1,741 gallons to the garden in a normal year (81.3% of its need).
If you buy one, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Portales's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,309 | 10,993 |
| 110 gal | 1,741 | 10,561 |
| 165 gal | 1,850 | 10,452 |
| 275 gal | 1,898 | 10,403 |
| 550 gal | 1,898 | 10,403 |
| 1,000 gal | 1,898 | 10,403 |
| 1,500 gal | 1,898 | 10,403 |
| 2,500 gal | 1,898 | 10,403 |
| 5,000 gal | 1,898 | 10,403 |
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 New Mexico?
Regulated through the State Engineer Office; no specific requirements exist for outdoor uses; indoor uses must meet quality standards; check county for local incentives
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