Using Harvested Rainwater for Laundry
A standard washing machine uses 15-30 gallons per load, while high-efficiency front-loaders use as little as 12-15 gallons. With the average household doing about one load per person per day, rainwater can significantly offset laundry water costs. Rainwater is naturally soft, which means you can use less detergent — up to 50% less than with hard municipal water. This softness also reduces mineral buildup in your washing machine, extending its lifespan. Like toilet flushing, connecting rainwater to your washing machine requires a dedicated non-potable plumbing line, pump system, and filtration. A sediment filter and carbon filter are recommended to remove any debris or tannins that could stain light-colored fabrics.
Laundry Potential by State
How much of your laundry demand can rainwater meet? It depends on where you live. The table below shows the annual harvest, demand coverage, and recommended tank size for laundry 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% | 2,500 gal | $98.55 |
| Texas | 28.9" | 22,277 gal | 100.0% | 2,500 gal | $54.75 |
| Florida | 54.5" | 39,622 gal | 100.0% | 5,000 gal | $54.75 |
| New York | 46.2" | 33,641 gal | 100.0% | 2,500 gal | $98.55 |
| Colorado | 15.9" | 11,589 gal | 100.0% | 1,000 gal | $54.75 |
| Hawaii | 63.7" | 45,229 gal | 100.0% | 5,000 gal | $164.25 |
| Arizona | 13.6" | 8,373 gal | 76.5% | 1,000 gal | $50.24 |
| Washington | 38.4" | 27,511 gal | 100.0% | 5,000 gal | $65.70 |
Setup Requirements for Laundry
Rainwater for laundry requires the same basic plumbing setup as toilet flushing — dedicated non-potable pipe, pump, pressure tank, and municipal backup — with the addition of better filtration. A sediment filter (5-20 micron) combined with an activated carbon filter removes fine particles and tannins that could discolor light-colored fabrics. The carbon filter also removes any taste or odor compounds.
The reward for this setup is significant: rainwater is naturally soft, meaning you can reduce detergent use by 30-50% and eliminate the need for fabric softener. Hard municipal water leaves mineral deposits that make fabrics stiff and dingy over time — rainwater avoids this entirely. Your washing machine also benefits from reduced scale buildup, potentially extending its lifespan. The connection point is typically a T-valve on the washing machine supply line that allows switching between rainwater and municipal supply.
Recommended Equipment
- Storage tank (500-1,000 gal, shared with toilet supply)
- Submersible pump with pressure tank
- 20-micron sediment filter + activated carbon filter
- Purple non-potable piping
- Municipal water backup with air gap
- T-valve for source switching at washer
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
- Car Washing — 50 gal/day
- Livestock Watering — 30 gal/day
- Pool Top-Off — 10 gal/day
- Drinking and Cooking — 1 gal/day (potable treatment required)
- General Outdoor Use — 30 gal/day
- Pressure Washing — 100 gal/day
Calculate Your Laundry Potential
Use our Rainwater Harvesting Calculator to see how much of your laundry demand can be met by rainwater in your specific location. Select laundry 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.