What Should You Do To Your Swimming Pool After It Rains?

Raindrops falling into the pool water next to the ladder underneath it.

Stormy weather especially with heavy rainfall and strong winds are quite common in the Midwest where I am as well as other parts of the country and world.  It can be sunny with clear skies one minute, then turn cloudy with pouring rain the next.

I have heard some pool owners say they have had problems after a major rainfall in keeping the pools chlorine and pH levels stable.  While a rain can and usually will affect your pools chemicals, you shouldn’t be worried each time rain is in the forecast.  I will go over a few things I do and sometimes do not do after a rain shower passes.

After a heavy rain the chlorine in your pool will become diluted.  Depending on the total rainfall you received, maintenance may or may not be required.  If you received substantial rainfall test your chlorine and pH levels, then add the products necessary to bring your levels back to normal.  Shocking your pool after a heavy rain is an easy way to ensure your swimming pool will not be adversely affected by the dilution caused by the rain storm.


After receiving a severe rain storm, the chlorine levels in your pool will be affected.  The amount of rain you received and how quickly it fell at once will play a major role in the affect it will have on your chlorine ppm.

In many cases, if you have a torrential downpour pass over your area, your chlorine level may completely zero out.  This means your water is no longer being sanitized and will become cloudy, foggy or even begin to form algae in a very short period of time.

In this case, it is best to act promptly to avoid any adverse affects from the rain storm.

  • Using your chlorine test kit of choice, check your current chlorine parts per million (ppm) that is in your swimming pools water.
  • If your test reveals a reading about 3 ppm or higher, you probably did not receive enough rain to cause any major issues to your swimming pools water, and require no chlorine adjustments.
  • Test results of 1 to 2 ppm on your chlorine test indicate a slight dilution and you may want to add a slightly higher chlorine dosage temporarily, and / or a small amount of shock to your pool to bring it back to the optimum levels of 3 to 5 ppm.
  • If you had an enormous amount of rain in a short period of time, you chlorine test may indicate that the rain actually zeroed out the chlorine inside your swimming pool.
    • Shock your pool at full strength to to regain your chlorine levels to above 3 ppm and continue your regular maintenance schedule afterwards and your pool will remain clear and clean as if no storm visited the area.


Rainfall also can negatively impact a pools pH balance.  Due to the acidic nature of natural rain water, your pH levels are likely going to drop after a decent amount of rainfall. 

pH LevelExamples
4.0Acid Rain Water
4.5Acid Lake Rain
5.6Clean Rain Water
7Pure Water
8Sea Water

The more acidic rain that occurred during your rain event, the lower you pH levels will have dropped.  You will need to test your waters pH balance with a test strip or testing kit to determine the current levels in your water.

  • Using your preferred testing kit, check your water pH balance a few inches below the swimming pools water surface.
  •  The optimum range desired would be somewhere between 7.2 and 7.6 ppm.  Slightly outside of this range, should be alright, but you will want to monitor your levels closely to ensure they don’t get farther from the recommended ranges.
  • If your levels are below 7.2, add Borax to bring your pH balance back to the recommended levels.
  • In the event that your levels are too high, Muriatic Acid can be used to lower the pH levels.

If you are unsure how much Borax or Muriatic acid you should be adding to your swimming pool, you can use the Pool Calculator.  This is a free and easy way to determine how much chemicals are required based on the volume of water in your pool to get the preferred range you desire.


I have heard of some people adding extra chlorine, shocking the water and even raising the pH in advance in the wake of a meteorologists forecast.

They do this with the mindset that as the predicted rainfall and storms arrive, the dilution of the water will not be as significant and keep the pool waters chlorine levels and pH in check. 

This sounds good, but below are three reasons why I DO NOT recommend this strategy.

The radar shows a big time super cell headed your way.  Several inches of rainfall are behind the storm and we are right in the path.

1. While meteorologists are incredibly talented and we depend on there expertise each day in helping us determine how to plan out door activities and prepare for dangerous storms, there is never any guarantee you will get as much rain as predicted.

Storms can change paths, strengthen, weaken or even completely dissipate without any reasoning.

2. Should the storm not bring as much rain as expected, the chemicals you added to your pool water cannot be removed.

If it doesn’t rain, your chlorine levels and pH balance are now going to be too high and require additional chemicals to reverse the process.  This can also leave swimmers on land instead of in the water until the levels are back to safe levels.

3. Money!  Pool chemicals are not cheap.  Even the most frugal pool owners that know how to cut costs don’t want to add something to their pool that they don’t have too.  In doing this, it will require added costs to replace them in the upcoming days.

Wait until after the storm as came and gone, test your water accordingly and add only the chemicals needed, safe money and start swimming right away.


If you had sustained heavy winds, hail or extremely heavy rain with your storm, you may need to remove leaves, branches and other debris from the water.

As extremely heavy rain falls, or especially hail stones, it rips the leaves and small limbs from trees in its path and sends them straight to the ground.  If the rain is falling sideways with a heavy wind, it will also cause these leaves and debris to blow throughout your yard.

This will unfortunately add unwanted he leafs, greens and stems in the water of your swimming pool.

Skimming the top of the water after a storm will help reduce the amount of leaves having to be caught by your skimmer.

Some of the leaves will  eventually make there way to the bottom of the pool and will need vacuumed and removed to bring the cleanliness of the pool back to normal.


If you had a substantial amount of rain and were unable to add the appropriate chlorine to the pool quick enough, you may have developed some algae.

If this is the case, you will need to shock your pool water, and add a treatment of algaecide.  This will kill all living bacteria including algae.

Wait about 24 hours until all the algae has died and is no longer green.

Scrub the side of the walls, bottom of the floor if needed, then vacuum it up once it settles to the bottom of the pool floor.

If you are not able to return your water to the crystal clear state it once was, you may also need to add some stabilizer which will clear up your pool once the algae is gone.


When draining the water, use either a designed drain plug that is equipped with your swimming pool, a submersible water pump or for sand filters use the waste setting on the filter to drain your water.

The backwash feature on sand filters should only be used when your pool needs backwashed.  Do no leave it set to backwash for several minutes simply to drain the pools water.


Above ground swimming pools that are overflowing should be drained so that the pool water level is back to its recommended range.  If water is above the top of the skimmer, it probably has too much water.

When water is over filled, it can pour down between the sides of the pool wall and liner allowing the excess water to wash away some sand or dirt from underneath the bottom.

Everyone that owns an above ground pool will at some point have this happen and there is no reason to worry, simply get the water levels back to normal and the water will dry out that ran down the walls. 


Some underground pools may have an overflow that automatically drains excess water preventing the pool from being overfull at any given time.  These type of pools require no draining do to excessive rain water.

Other underground pools may need to be drained slightly so that the water is at the proper height with the pools skimmer for optimum pump performance.  In most cases, underground pools will not be harmed by excessive water or heavy rains.

Since these pools are beneath the ground, draining them are not completely necessary.


Sometimes during the spring or summer months we may get a quick 10 or 15 minute rain shower, or even a soothing light rain that you wouldn’t have even noticed occurred if you didn’t go out and see the wet sidewalks and grass.

These very minimal rain showers that have little to no measurement on your rain gauge will have the same affect on your pool water and should not require any testing or alterations in your weekly regular pool maintenance.

As a matter of fact, as long as there is no threat of lightning or thunder, this could be one of the best swimming times of the season.  Lounging in the warm pool water while cool and small rain drops fall from above can be a relaxing and soothing way to enjoy your swimming pool from time to time.

Only measurable amounts of rainfall, in a short period of time will have a major affect on your pools water.  However, if you have had steady rain falling for several hours or multiple days, this too could cause your water to need added chlorine or pH adjustments due to the amount of water that has fallen from the sky.

Recent Posts