Heavy rain might seem harmless, but when it hits your pool, it can throw everything out of balance. After a storm, your pool might look full and fresh — but chances are it’s packed with debris, diluted chemicals, and off-balance water chemistry.
In this guide, we explain how to manage rainwater in your pool after a storm, step-by-step, to bring your water back to safe and swimmable condition fast.
What Rainwater Does to Your Pool
Rainwater can:
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Lower pH and alkalinity
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Dilute chlorine and other chemicals
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Bring in contaminants like dirt, leaves, oils, and bacteria
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Increase water level beyond safe limits
Stormwater run-off also introduces phosphates and nitrates — nutrients that algae love.
Step-by-Step: What to Do After a Storm
1. Turn Off Power to Your Pool Equipment
Before inspecting or cleaning, switch off all equipment to avoid damage or electrical hazards.
2. Clear Debris from the Surface and Skimmer
Use a leaf rake or net to remove:
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Leaves
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Twigs
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Insects
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Other debris floating on the surface
Empty the skimmer and pump baskets.
3. Check and Adjust Water Level
If your pool is overflowing:
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Drain excess water to the halfway point on the skimmer opening
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Use the waste setting on your multiport valve, if available
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If no valve, use a submersible pump or manual siphon
Don’t let your pool overflow onto paving — it can wash chemicals into your garden or drainage.
4. Vacuum the Pool
After the surface is clear, vacuum debris from the bottom.
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Use a manual vacuum or your automatic cleaner
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If water is cloudy, use the “waste” setting to vacuum out dirty water directly
5. Brush the Walls and Steps
Rain can stir up bacteria and algae spores. Brush all surfaces to dislodge particles and prevent growth.
6. Test the Water
Rain affects:
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Chlorine – Diluted and less effective
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pH – Usually drops due to acidic rain
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Alkalinity – Often reduced
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Calcium hardness – May decrease
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Phosphates – Can increase from runoff
Use test strips or a kit to check all levels. We stock reliable test kits in our pool products section.
7. Rebalance Chemicals
Once tested:
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Add chlorine (or shock) to kill bacteria
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Adjust pH and alkalinity as needed
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Use algaecide if algae growth starts
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Add phosphate remover if levels are high
8. Run the Filter System Continuously for 24 Hours
Help the water circulate and clean fully. Backwash or clean the filter once water clears.
9. Retest After 24 Hours
Double-check chemical levels to ensure they’re back in balance.
10. Resume Normal Schedule
If everything looks good, return to your normal maintenance schedule. Monitor closely for the next few days.
How to Prevent Rain Damage in Future
| Prevention Tip | Why It Helps |
|---|---|
| Use a pool cover | Reduces water dilution and debris |
| Build landscaping slopes away from the pool | Limits run-off contamination |
| Maintain good drainage | Avoids flooding around equipment |
| Add extra chlorine before storms | Preps the water for contamination |
| Clean filters regularly | Ensures they handle the post-storm load |
Conclusion
Rainwater in your pool after a storm isn’t just harmless water — it dilutes chlorine, changes your chemistry, and introduces contamination.
The fix? Clean the debris, test the water, rebalance your chemicals, and let your filter system do its job.
Need test kits, shock treatments or debris removal tools? Browse our full pool products selection or ask our team in-store for expert help.
FAQ
Not always. Rainwater can reduce chlorine and introduce bacteria. Test and rebalance the water before swimming to avoid skin or eye irritation and infection risks.
Most rainwater is slightly acidic, so it tends to lower pool pH. This can make the water more corrosive and reduce chlorine effectiveness.
Clear debris, check water level, test chemical balance, adjust chlorine, pH, and alkalinity, and run the pump continuously for 24 hours.
Yes, it’s recommended to shock the pool after heavy rain to kill off contaminants and restore chlorine levels quickly.
Use the “waste” setting on your filter, a submersible pump, or manual siphon to drain excess water. Stop when water sits halfway up the skimmer opening.
Cloudiness comes from fine debris, bacteria, diluted chlorine, and imbalanced pH. Run your filter and shock the pool to clear it up.
Run the pump continuously for 24 hours after a storm to clear and circulate the water, especially if you’ve added shock or other chemicals.
Yes. Rain can introduce spores, phosphates, and nutrients that promote algae growth. Pre-emptive algaecide and brushing helps control it.
Rain can slightly dilute calcium levels. Test and adjust if your water becomes too soft, especially for concrete or plaster pools.
Check our [pool products](https://www.pumpandpoolpeople.com.au/) page for test kits, shock, algaecides, phosphate removers, skimmers, and pumps.