Rainwater Harvesting in Oregon
Oregon (OR) receives an average of 27.4 inches of rainfall per year, placing it in the low-rainfall category among US states. The wettest month is typically Dec, and the driest is Jul. Rainwater harvesting is fully legal in Oregon. A standard 1,500-square-foot asphalt shingle roof can collect approximately 22,950 gal per year, saving an estimated $64.20 annually at the state's average municipal water rate of 0.6 cents per gallon.
Monthly Rainfall in Oregon
Understanding Oregon's monthly rainfall distribution is essential for sizing your storage tank correctly. The table below shows average monthly rainfall and the resulting harvest from a 1,500-square-foot roof. While Oregon's 27.4 inches of annual rainfall is moderate, efficient collection from a well-designed system still produces thousands of gallons. Focus on maximizing collection efficiency with a metal roof and capturing every rain event.
| Month | Rainfall (in) | Harvest (1,500 sq ft) |
|---|---|---|
| Jan | 4.8" | 3,588 gal |
| Feb | 3.8" | 2,841 gal |
| Mar | 3.4" | 2,542 gal |
| Apr | 2.4" | 1,794 gal |
| May | 2.0" | 1,495 gal |
| Jun | 1.2" | 897 gal |
| Jul | 0.4" | 299 gal |
| Aug | 0.5" | 374 gal |
| Sep | 0.8" | 598 gal |
| Oct | 2.0" | 1,495 gal |
| Nov | 4.4" | 3,289 gal |
| Dec | 5.0" | 3,738 gal |
| Total | 27.4" | 22,950 gal |
Harvest by Roof Size in Oregon
Your actual harvest depends on how much roof area you connect to your collection system. Not every square foot of your roof needs to drain into your tank — many homeowners start by connecting just one or two downspouts covering a portion of their roof. The table below shows what different collection areas yield annually in Oregon using an asphalt shingle roof at 80% efficiency.
| Roof Area | Annual Harvest | Rec. Tank Size | Annual Savings |
|---|---|---|---|
| 1,000 sq ft | 15,301 gal | 2,500 gal | $64.20 |
| 1,500 sq ft | 22,950 gal | 5,000 gal | $64.20 |
| 2,000 sq ft | 30,602 gal | 5,000 gal | $64.20 |
| 2,500 sq ft | 38,251 gal | 10,000 gal | $64.20 |
Upgrading to a metal roof (95% efficiency) boosts collection by about 19% compared to asphalt shingle. For example, a 1,500-square-foot metal roof in Oregon captures approximately 27,255 gal per year when used for garden irrigation and toilet flushing for a household of two.
Rainwater Harvesting Laws in Oregon
Oregon allows rainwater collection from rooftop surfaces without a permit. A 2009 law clarified that rooftop collection does not require a water right. Underground cisterns may require building permits.
Regulation Summary for Oregon
- Legal Status: Legal — no restrictions
- Max Collection: No limit
- Permit Required: No — for standard residential systems
- Municipal Water Rate: 0.6 cents per gallon (state average)
Popular Uses for Harvested Rainwater in Oregon
Oregon homeowners use harvested rainwater for a variety of purposes. The most common applications are garden irrigation, lawn watering, and toilet flushing. Each use has different water requirements and may require different levels of filtration. Explore detailed guides for the most popular uses in Oregon:
How Oregon Compares to Similar States
The table below compares Oregon with five states that have similar annual rainfall patterns. All calculations use a standard 1,500-square-foot asphalt shingle roof collecting water for garden irrigation.
| State | Annual Rainfall | Legal Status | Annual Harvest | Water Cost | Annual Savings |
|---|---|---|---|---|---|
| Oregon | 27.4" | Legal | 22,950 gal | 0.6 c/gal | $64.20 |
| Kansas | 28.9" | Legal | 21,980 gal | 0.5 c/gal | $53.50 |
| Texas | 28.9" | Legal | 22,277 gal | 0.5 c/gal | $53.50 |
| Nebraska | 24.2" | Legal | 18,167 gal | 0.4 c/gal | $42.80 |
| Minnesota | 30.6" | Legal | 22,725 gal | 0.5 c/gal | $53.50 |
| California | 22.2" | Legal | 13,756 gal | 0.9 c/gal | $96.30 |
Tips for Rainwater Harvesting in Oregon
With moderate rainfall of 27.4 inches per year, Oregon requires a more strategic approach to rainwater harvesting. Maximize your collection efficiency by using the largest possible roof area and choosing a high-efficiency roof material like metal (95% capture rate). Size your tank to store at least one month's harvest to bridge typical dry periods. A 1,000-gallon tank is a good starting point for most Oregon homeowners. Connect the tank to a drip irrigation system for maximum efficiency — drip systems use 30-50% less water than sprinklers. In drier months, prioritize high-value uses like vegetable gardens over lawn irrigation.
Calculate Your Specific Harvest in Oregon
The estimates above use standardized assumptions. Use our Rainwater Harvesting Calculator to enter your exact roof area, material, household size, and intended uses for a customized analysis tailored to your property in Oregon. You can also browse all states to compare potential across the country, or explore tank sizes and water uses for detailed information on system components and water budgeting.