How Does Rain Affect My Pool Water?

rain pool water

Rain may provide quite the show as it pours across your pool, but there is a different story happening under the water.

Why does rain change my pool water’s chemistry?

First, let us explain the complexity of rain. It can have different levels of acidity, depending on where you live. The acidity in rain is primarily caused by man-made activities: the burning of fossil fuels to generate electricity, vehicles and manufacturing, oil refineries and other industries. Rain with higher acidity will cause your pool’s pH level to drop. The Total Alkalinity will begin working to keep your pH in balance. Chlorine will also be consumed while attacking the new pollutants.

What to do after a heavy rainfall:

First, remove any excess water down to the recommended level

This can be done by setting your D.E. or Sand Filter to waste, which will bypass your filter system. If this is not an option, you can rent a submersible sump pump from your local hardware store to lower the water level. Since you only need to drain up-to a few inches of water, we recommend setting the sump pump on your stairs or in the shallow end. Also, be careful not to drop the water level below your skimmer opening.

Clean your pool
  • Skim the water surface of all leaves, twigs and debris
  • Empty your Skimmer Basket
  • Use a Leaf Rake to remove any debris that may have sank to the bottom of your pool
  • Brush and Vacuum the walls and floor
  • Backwash or clean the Filters (cleaning method differs between pool filter-type)
Test and adjust chemical levels

Rain can be very acidic, which will quickly drop your pool’s pH level. The drop in pH will also impact the total alkalinity and chlorine levels.

  • Check water chemistry with a Test Kit
  • A pH Increaser will be needed in most cases to bring your pH level to a safe level (between 7.4 to 7.8). If pH is too low, the water may become corrosive. If pH is too high, it will hinder the effectiveness of your chlorine.
  • Alkalinity Increaser will help stabilize the pH balance in your pool. This will also help protect against equipment corrosion and plaster etching caused by low alkalinity. Safe range between 80-120 ppm.
  • It is not uncommon to see cloudy water after a heavy downpour. Try adding a Water Clarifier to your water, which will coagulate dirt and oil that are clouding the water.
  • It is also a good idea to add an Algaecide to your water at this point. This will neutralize any potential algae blooms that were introduced from the rain.
Check the chlorine level

Chlorine will be consumed quickly while fighting the contaminants, so you may need to Shock the pool after a heavy rainfall. This will super-chlorinate the water and kill any remaining pollutants.

Run the filter system

It is important to run the Pump for 8-10 hours to circulate the water and distribute the chemicals throughout your pool.

Now that your pool has weathered the storm, it’s time to go enjoy the sunshine!

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Brian Champ
When Brian isn't writing pool-related articles, he enjoys anything that will take him outdoors: hiking, biking and trail running ...to name a few. Brian is excited to share his pool knowledge with helpful how-to guides, product reviews, comparisons, and more!