Rainwater Harvesting by State
Compare rainwater harvesting potential across all 50 US states and the District of Columbia. Each state's calculation uses a standard 1,500-square-foot asphalt shingle roof to provide a consistent comparison. Actual harvest depends on your specific roof area, material, and local rainfall patterns. Click any state for a detailed breakdown including monthly rainfall, legal status, tank recommendations, and water cost savings specific to that location.
Legal Status Overview
Rainwater harvesting is explicitly legal or unrestricted in 49 states and the District of Columbia. Only 2 states (Colorado, Utah) have significant restrictions on collection volumes. The trend across the country is toward greater permissiveness, with several states that previously restricted collection now allowing it. Many states actively incentivize rainwater harvesting through tax credits, rebates, and building code provisions.
All States Ranked by Annual Rainfall
The table below ranks every state by average annual rainfall, showing the estimated harvest from a standard 1,500-square-foot asphalt shingle roof. States with more rainfall naturally produce more harvestable water, but even low-rainfall states like Arizona and Nevada can meaningfully benefit from collection systems due to their high water costs and acute need for conservation.
| # | State | Annual Rainfall | Legal Status | Annual Harvest (1,500 sq ft) | Water Cost | Annual Savings |
|---|---|---|---|---|---|---|
| 1 | Hawaii (HI) | 63.7" | Legal | 45,229 gal | 1.5 c/gal | $160.50 |
| 2 | Louisiana (LA) | 60.1" | Legal | 46,201 gal | 0.4 c/gal | $42.80 |
| 3 | Mississippi (MS) | 56.9" | Legal | 41,865 gal | 0.4 c/gal | $42.80 |
| 4 | Alabama (AL) | 56" | Legal | 40,371 gal | 0.5 c/gal | $53.50 |
| 5 | Florida (FL) | 54.5" | Legal | 39,622 gal | 0.5 c/gal | $53.50 |
| 6 | Tennessee (TN) | 53.7" | Legal | 38,274 gal | 0.4 c/gal | $42.80 |
| 7 | Georgia (GA) | 50.7" | Legal | 36,108 gal | 0.6 c/gal | $64.20 |
| 8 | Arkansas (AR) | 50.6" | Legal | 37,827 gal | 0.4 c/gal | $42.80 |
| 9 | Connecticut (CT) | 50.3" | Legal | 35,811 gal | 0.8 c/gal | $85.60 |
| 10 | North Carolina (NC) | 50.3" | Legal | 35,584 gal | 0.5 c/gal | $53.50 |
| 11 | South Carolina (SC) | 49.8" | Legal | 35,885 gal | 0.5 c/gal | $53.50 |
| 12 | Kentucky (KY) | 48.9" | Legal | 35,883 gal | 0.4 c/gal | $42.80 |
| 13 | Rhode Island (RI) | 47.9" | Legal | 34,836 gal | 0.7 c/gal | $74.90 |
| 14 | Massachusetts (MA) | 47.7" | Legal | 33,940 gal | 0.8 c/gal | $85.60 |
| 15 | Maine (ME) | 47.3" | Legal | 34,090 gal | 0.6 c/gal | $64.20 |
| 16 | New Jersey (NJ) | 47.1" | Legal | 34,687 gal | 0.7 c/gal | $74.90 |
| 17 | New Hampshire (NH) | 47" | Legal | 33,490 gal | 0.6 c/gal | $64.20 |
| 18 | New York (NY) | 46.2" | Legal | 33,641 gal | 0.9 c/gal | $96.30 |
| 19 | Delaware (DE) | 45.7" | Legal | 33,119 gal | 0.6 c/gal | $64.20 |
| 20 | West Virginia (WV) | 45.2" | Legal | 32,296 gal | 0.4 c/gal | $42.80 |
| 21 | Virginia (VA) | 44.3" | Legal | 31,997 gal | 0.6 c/gal | $64.20 |
| 22 | Pennsylvania (PA) | 43.6" | Legal | 31,547 gal | 0.6 c/gal | $64.20 |
| 23 | Maryland (MD) | 43.4" | Legal | 31,848 gal | 0.7 c/gal | $74.90 |
| 24 | Vermont (VT) | 42.7" | Legal | 30,052 gal | 0.6 c/gal | $64.20 |
| 25 | Indiana (IN) | 42.4" | Legal | 31,323 gal | 0.4 c/gal | $42.80 |
| 26 | Missouri (MO) | 42.2" | Legal | 30,651 gal | 0.5 c/gal | $53.50 |
| 27 | District of Columbia (DC) | 40.8" | Legal | 29,754 gal | 0.9 c/gal | $96.30 |
| 28 | Ohio (OH) | 39.6" | Legal | 29,155 gal | 0.5 c/gal | $53.50 |
| 29 | Illinois (IL) | 39.2" | Legal | 29,080 gal | 0.6 c/gal | $64.20 |
| 30 | Washington (WA) | 38.4" | Legal | 27,511 gal | 0.6 c/gal | $64.20 |
| 31 | Oklahoma (OK) | 36.5" | Legal | 27,512 gal | 0.4 c/gal | $42.80 |
| 32 | Iowa (IA) | 35.9" | Legal | 26,540 gal | 0.5 c/gal | $53.50 |
| 33 | Michigan (MI) | 34.7" | Legal | 25,119 gal | 0.6 c/gal | $64.20 |
| 34 | Wisconsin (WI) | 33.2" | Legal | 24,221 gal | 0.5 c/gal | $53.50 |
| 35 | Minnesota (MN) | 30.6" | Legal | 22,725 gal | 0.5 c/gal | $53.50 |
| 36 | Kansas (KS) | 28.9" | Legal | 21,980 gal | 0.5 c/gal | $53.50 |
| 37 | Texas (TX) | 28.9" | Legal | 22,277 gal | 0.5 c/gal | $53.50 |
| 38 | Oregon (OR) | 27.4" | Legal | 22,950 gal | 0.6 c/gal | $64.20 |
| 39 | Nebraska (NE) | 24.2" | Legal | 18,167 gal | 0.4 c/gal | $42.80 |
| 40 | California (CA) | 22.2" | Legal | 13,756 gal | 0.9 c/gal | $96.30 |
| 41 | Alaska (AK) | 22" | Legal | 15,176 gal | 1.2 c/gal | $128.40 |
| 42 | South Dakota (SD) | 20.1" | Legal | 14,655 gal | 0.5 c/gal | $53.50 |
| 43 | Idaho (ID) | 18.9" | Legal | 11,514 gal | 0.4 c/gal | $42.80 |
| 44 | North Dakota (ND) | 17.8" | Legal | 12,934 gal | 0.5 c/gal | $53.50 |
| 45 | Colorado (CO) | 15.9" | Restricted | 11,589 gal | 0.5 c/gal | $53.50 |
| 46 | Montana (MT) | 15.3" | Legal | 10,692 gal | 0.5 c/gal | $53.46 |
| 47 | New Mexico (NM) | 14.6" | Legal | 9,047 gal | 0.7 c/gal | $63.33 |
| 48 | Arizona (AZ) | 13.6" | Legal | 8,373 gal | 0.6 c/gal | $50.24 |
| 49 | Wyoming (WY) | 12.9" | Legal | 8,748 gal | 0.5 c/gal | $43.74 |
| 50 | Utah (UT) | 12.2" | Restricted | 9,421 gal | 0.4 c/gal | $37.68 |
| 51 | Nevada (NV) | 9.5" | Legal | 5,683 gal | 0.7 c/gal | $39.78 |
How We Calculate State Harvest Estimates
Our rainwater harvesting calculations use NOAA climate normal data for monthly rainfall distribution across each state. We apply the standard formula: roof area (square feet) multiplied by rainfall (inches) multiplied by 0.623 (the conversion factor for gallons per square foot per inch) multiplied by the roof material's collection efficiency. For the comparison table above, we use a uniform 1,500-square-foot asphalt shingle roof (80% efficiency) to ensure fair comparisons between states.
Water cost savings are calculated using each state's average municipal water rate, which ranges from about $0.002 per gallon in low-cost states to over $0.015 per gallon in Hawaii. These are average statewide figures — your actual rate may be higher or lower depending on your specific water utility. Many utilities use tiered pricing where the per-gallon cost increases as you use more water, making rainwater harvesting even more valuable for high-consumption households since it offsets the most expensive tier of usage.
Monthly rainfall patterns matter significantly. A state receiving 40 inches of rain concentrated in spring months will need larger tank storage than a state with the same annual total spread evenly throughout the year. Our calculator provides month-by-month breakdowns to help you understand your specific seasonal supply and demand balance and choose the right tank size accordingly.
Regional Insights
Southeast: States like Louisiana, Mississippi, Alabama, and Florida receive 50-65 inches of annual rainfall, offering the highest raw harvest potential. The challenge is concentrated summer rainfall — heavy seasonal rains require adequate tank storage to bridge drier periods. The good news is that water demand for irrigation also peaks during summer when rain is most abundant.
Northeast: New England and Mid-Atlantic states receive 40-50 inches of relatively well-distributed rainfall. This consistent pattern means smaller tanks can be effective, as dry spells between rain events are typically short. Higher municipal water rates in states like Massachusetts, Connecticut, and New Jersey increase the financial benefit of harvesting.
Midwest: The Great Plains and upper Midwest see moderate rainfall (25-42 inches) with strong seasonal variation. Spring and early summer rains provide the bulk of the harvest, while late summer and fall can be dry. Tank sizing should bridge a potential 6-8 week dry period in late summer.
West: Western states vary enormously. The Pacific Northwest coast gets 30-50 inches but concentrated in winter, while the interior Southwest receives under 15 inches. Oregon and Washington collect abundantly in winter but face bone-dry summers — large tanks are essential. Arizona and New Mexico have low totals but strongly encourage harvesting due to critical water scarcity.