Using Harvested Rainwater for Drinking and Cooking
Using harvested rainwater for drinking and cooking requires the most rigorous treatment of any residential use. Each person consumes roughly 0.5-1 gallon per day for drinking and cooking combined. Proper treatment includes a first-flush diverter (discards the initial dirty roof wash), sediment filtration (5-micron minimum), activated carbon filtration (removes organic compounds and improves taste), and ultraviolet (UV) sterilization to eliminate bacteria, viruses, and protozoa. Some systems add a final 0.5-micron absolute filter for added safety. The roof material must be potable-safe — metal, clay tile, concrete tile, or slate. Asphalt shingle and wood shake roofs leach chemicals that make water unsuitable for drinking even after filtration. Regular water quality testing (at least annually) is strongly recommended. Many off-grid homes in Hawaii, the Pacific Northwest, and rural Appalachia rely on properly treated rainwater as their sole drinking water source.
Drinking and Cooking Potential by State
How much of your drinking and cooking demand can rainwater meet? It depends on where you live. The table below shows the annual harvest, demand coverage, and recommended tank size for drinking and cooking in eight representative states, using a 1,500-square-foot asphalt shingle roof and a household of 2.
| State | Annual Rainfall | Annual Harvest | Demand Met | Rec. Tank | Savings/Year |
|---|---|---|---|---|---|
| California | 22.2" | 13,756 gal | 100.0% | 5,000 gal | $6.57 |
| Texas | 28.9" | 22,277 gal | 100.0% | 5,000 gal | $3.65 |
| Florida | 54.5" | 39,622 gal | 100.0% | 10,000 gal | $3.65 |
| New York | 46.2" | 33,641 gal | 100.0% | 5,000 gal | $6.57 |
| Colorado | 15.9" | 11,589 gal | 100.0% | 2,500 gal | $3.65 |
| Hawaii | 63.7" | 45,229 gal | 100.0% | 5,000 gal | $10.95 |
| Arizona | 13.6" | 8,373 gal | 100.0% | 2,500 gal | $4.38 |
| Washington | 38.4" | 27,511 gal | 100.0% | 5,000 gal | $4.38 |
Setup Requirements for Drinking and Cooking
Potable rainwater requires the most comprehensive treatment chain of any residential application. The roof material must be potable-safe (metal, clay tile, concrete tile, or slate — never asphalt shingle or wood shake). Every component from the roof to the glass must be designed to maintain water quality.
The treatment system typically includes: (1) a first-flush diverter discarding the first 1 gallon per 100 square feet of roof, (2) a 20-micron pre-filter catching coarse debris, (3) a 5-micron sediment filter removing fine particles, (4) an activated carbon filter removing chlorine, organic compounds, and improving taste, (5) UV sterilization killing bacteria, viruses, and protozoa, and optionally (6) a 0.5-micron absolute filter as a final safety measure. Test your water at least annually for coliform bacteria, pH, turbidity, and basic chemistry. Many states and counties offer free or low-cost water testing through their health departments.
Treatment Chain
- Potable-safe roof material (metal, clay, concrete, or slate)
- First-flush diverter (1 gal per 100 sq ft of roof)
- 20-micron pre-filter
- 5-micron sediment filter
- Activated carbon filter (taste, organics)
- UV sterilizer (40 mJ/cm2 minimum dose)
- Optional: 0.5-micron absolute filter
- Annual water quality testing
Other Rainwater Uses
Explore other ways to use harvested rainwater at home:
- Garden Irrigation — 50 gal/day
- Lawn Irrigation — 75 gal/day
- Toilet Flushing — 20 gal/day
- Laundry — 15 gal/day
- Car Washing — 50 gal/day
- Livestock Watering — 30 gal/day
- Pool Top-Off — 10 gal/day
- General Outdoor Use — 30 gal/day
- Pressure Washing — 100 gal/day
Calculate Your Drinking and Cooking Potential
Use our Rainwater Harvesting Calculator to see how much of your drinking and cooking demand can be met by rainwater in your specific location. Select drinking and cooking from the use checkboxes along with any other uses you are considering, and get a personalized monthly supply vs. demand analysis with tank size recommendation and cost savings estimate.