Asphalt Shingle Roof for Rainwater Harvesting
Asphalt Shingle roofing captures 80% of rainfall that hits its surface, making it a moderately efficient material for rainwater harvesting. A 1,500-square-foot asphalt shingle roof in Texas (29 inches annual rainfall) collects approximately 22,277 gal per year. Asphalt Shingle is not recommended for potable water collection due to potential chemical leaching. It is well-suited for non-potable uses including garden irrigation, lawn watering, toilet flushing, and general outdoor use.
About Asphalt Shingle Roofing for Rainwater Collection
Asphalt shingle is the most common residential roofing material in the United States, covering approximately 75-80% of homes. With a collection efficiency of 80%, it is a moderately effective rainwater harvesting surface. The 20% efficiency loss comes from the granulated surface texture that retains water through surface tension and absorption, particularly during light rainfall events.
The primary concern with asphalt shingle roofing for rainwater harvesting is its chemical composition. Asphalt shingles contain petroleum-based compounds, mineral granules (typically crusite, a form of calcium carbonate with ceramic coating), and various binders that can leach into collected water. For this reason, asphalt shingle roofs are not recommended for potable water collection, even with filtration. However, they are perfectly suitable for non-potable uses: garden irrigation, lawn watering, toilet flushing, laundry, car washing, and all other outdoor applications.
To maximize water quality from asphalt shingle roofs, use a first-flush diverter to discard the first gallon per 100 square feet of roof during each rain event. This eliminates the most concentrated contaminants that wash off during the initial runoff. Additionally, allow new asphalt shingle roofs to weather for at least 6 months before beginning rainwater collection, as fresh shingles release the most compounds during their first few months of exposure.
Harvest Potential by State with Asphalt Shingle
The table below shows the annual rainwater harvest from a 1,500-square-foot asphalt shingle roof (80% efficiency) across six representative states. Annual rainfall varies dramatically across the country, and this variation directly affects your collection potential.
| State | Annual Rainfall | Annual Harvest | Annual Savings |
|---|---|---|---|
| California | 22.2" | 13,756 gal | $96.30 |
| Texas | 28.9" | 22,277 gal | $53.50 |
| Florida | 54.5" | 39,622 gal | $53.50 |
| New York | 46.2" | 33,641 gal | $96.30 |
| Arizona | 13.6" | 8,373 gal | $50.24 |
| Washington | 38.4" | 27,511 gal | $64.20 |
Maintenance Tips for Asphalt Shingle Collection Roofs
Inspect your asphalt shingle roof twice per year for loose or damaged shingles that could contribute excess granules to your collected water. Clean gutters quarterly to remove accumulated granules, leaves, and debris. After significant storms, check for and remove any large debris that may have landed on the roof. Replace the first-flush diverter chamber at least annually, as asphalt granules can clog the drain valve. Monitor the color and sediment content of your collected water — if it appears dark or has a petroleum sheen, increase your first-flush volume or check for deteriorating shingles.
Compare Other Roof Materials
- Metal Roofing — 95% efficiency, potable safe
- Slate — 90% efficiency, potable safe
- Clay Tile — 85% efficiency, potable safe
- Concrete Tile — 85% efficiency, potable safe
- Wood Shake — 75% efficiency, non-potable only
Not sure which material is best for your needs? Use our calculator to compare harvest estimates for different roof materials with your specific roof area and location.