Using Harvested Rainwater for Pool Top-Off
Swimming pools lose water continuously through evaporation, splash-out, backwashing, and swimmer carryout. The average pool loses about 0.25 inches of water per day to evaporation — approximately 10-15 gallons for a standard 12x24-foot pool. In hot, arid climates, evaporation losses can exceed 25 gallons per day. Using harvested rainwater to maintain pool water levels reduces municipal water consumption and is straightforward to implement. Rainwater has low mineral content, which can reduce the need for pH adjustment chemicals. A simple float valve connected to your rainwater tank can automate the top-off process. Pool covers reduce evaporation by up to 95% and are the most effective complement to a rainwater-fed pool maintenance system.
Pool Top-Off Potential by State
How much of your pool top-off demand can rainwater meet? It depends on where you live. The table below shows the annual harvest, demand coverage, and recommended tank size for pool top-off in eight representative states, using a 1,500-square-foot asphalt shingle roof .
| State | Annual Rainfall | Annual Harvest | Demand Met | Rec. Tank | Savings/Year |
|---|---|---|---|---|---|
| California | 22.2" | 13,756 gal | 100.0% | 5,000 gal | $19.26 |
| Texas | 28.9" | 22,277 gal | 100.0% | 2,500 gal | $10.70 |
| Florida | 54.5" | 39,622 gal | 100.0% | 10,000 gal | $10.70 |
| New York | 46.2" | 33,641 gal | 100.0% | 5,000 gal | $19.26 |
| Colorado | 15.9" | 11,589 gal | 100.0% | 1,500 gal | $10.70 |
| Hawaii | 63.7" | 45,229 gal | 100.0% | 5,000 gal | $32.10 |
| Arizona | 13.6" | 8,373 gal | 100.0% | 1,500 gal | $12.84 |
| Washington | 38.4" | 27,511 gal | 100.0% | 5,000 gal | $12.84 |
Setup Requirements for Pool Top-Off
Using rainwater to top off your swimming pool is a straightforward application that saves hundreds of gallons per month in evaporation losses alone. The simplest approach is a manual fill: connect a hose from your rain barrel or tank to the pool fill point and add water as needed. For automation, install a float valve in the pool skimmer box connected to your rainwater tank through a small pump — the valve opens when water drops below a set level and closes when it reaches the target.
Rainwater actually benefits pool chemistry: its low mineral content means less calcium buildup and reduced need for pH adjustment chemicals compared to hard municipal water. No special filtration is needed for pool use since the pool's own filtration and chemical treatment system handles any minor impurities. A pool cover is the best complement to a rainwater top-off system, reducing evaporation by up to 95% and dramatically cutting the amount of makeup water needed.
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
- Drinking and Cooking — 1 gal/day (potable treatment required)
- General Outdoor Use — 30 gal/day
- Pressure Washing — 100 gal/day
Calculate Your Pool Top-Off Potential
Use our Rainwater Harvesting Calculator to see how much of your pool top-off demand can be met by rainwater in your specific location. Select pool top-off 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.