How Rain Water Affects Your Pool Water

Why Rain Changes Your Pool Water

Rain water is naturally soft and slightly acidic.

When it falls into your pool it can:

• Dilute chlorine or other sanitizers, making them less effective
• Lower the pH and total alkalinity, which can cause corrosion or etching
• Add phosphates, nitrates, pollen, and debris that feed algae growth
• Increase water level and overflow, which can wash dirt and contaminants into the pool

Immediate Steps After Heavy Rain

• Clear Out Debris Skim leaves, insects, and other material brought in by the rain. Clean skimmer and pump baskets.
• Check and Adjust Water Level If the water is too high, backwash or drain down to the middle of the skimmer opening. This keeps skimming action effective.
• Run the Pump and Filter Circulate the water for several hours to remove contaminants and re-mix chemicals.

Test and Balance Your Water

• Chlorine/Sanitizer: Rain dilutes chlorine. Test and raise back to the proper level (usually 1–3 ppm for chlorine pools, 30–50 ppm for salt pools’ stabilizer).
• pH and Alkalinity: Acidic rain lowers these levels. Test and add alkalinity increaser or pH increaser if needed.
• Calcium Hardness: Usually not affected immediately, but test if you’re seeing scaling or cloudy water.
• Stabilizer (Cyanuric Acid): Heavy rain can dilute stabilizer. Add if it’s fallen below your target range.

Shock or Superchlorinate

If the rainstorm was severe or the pool looks dull or cloudy afterward, add a shock treatment according to label directions to kill off bacteria and algae spores.

Preventive Tips

• Cover the Pool: A properly fitted cover keeps rain and debris out.
• Maintain Balanced Water: A well-balanced pool recovers faster after rain.
• Clean Surroundings: Keeping deck areas free of dirt and leaves reduces what washes in during storms.