There’s nothing quite like enjoying your pool with your family on a bright sunny day. But what happens when it rains? A swimming pool must be maintained properly so that you and your family can continue enjoying that fresh, cool water all summer long. If it is not maintained correctly, you will incur hidden pool costs in chemicals and other upkeep. That’s why it is essential to understand how to maintain a pool and its equipment and how the weather affects your pool’s water. If you know what to expect, you can take proactive measures and quickly check for any problems after rain or other severe weather events.

What Does Rainwater Do to My Pool? 

So, how does rain affect pool water? Minor rainfalls are unlikely to alter your pool’s water significantly. However, heavy or continuous downpours, living in a region that receives significant rain throughout the year, or even living in an area that is simply getting more rain than usual, can all affect your pool in different ways. You must monitor your pool’s water and chemical levels closely after rain.

To begin with, large amounts of rain can raise your pool’s water level, which makes it difficult for the skimmer to do its job effectively. Furthermore, excess water will dilute the chemicals in your pool water. Balancing chemicals in your pool is a delicate act. When one chemical is affected, it creates a ripple effect, altering other chemical levels. Any of these situations can cause a variety of issues if not monitored and treated quickly.

Impact to pH

When pH levels are outside of the ideal range of 7.4 – 7.6, chlorine performance is affected. The CDC recommends that a backyard pool maintain a pH of 7.2 – 7.8 to help disinfect the water and kill any bacteria that make their way into your pool. In addition to health concerns from bacteria, if pH levels are too low, it can also cause skin and eye irritation, among other problems.

However, rainwater is mildly acidic. In some regions, particularly the Northeastern and Midwestern United States, the rain is more acidic than typical rain. Because rainwater has a lower pH level than your pool, it can begin to lower your pool’s pH after heavy or consistent rains.


Rain will also dilute your pool’s alkalinity level. Alkalinity is important for your pool water because it is a pH stabilizer. When the pool’s alkalinity is at an appropriate level, the pH level will fluctuate less. 

If your pool’s pH and alkalinity levels are too low, the water can become corrosive. This can potentially cause damage to underwater metal surfaces like your ladders, rails, or pool lights. Corrosive water can also be detrimental to pool equipment. Monitoring your pool water after rainfall will help ensure that the alkalinity is at an appropriate level, which is a preventative measure for protecting your pool equipment and the money you have invested.

Calcium Readings

Rainwater is naturally soft. If your pool water is already soft before the rain, rainwater can cause calcium hardness to decrease. You may need to add Calcium Hardness to reach the appropriate level. Of course, suppose your pool water is already hard. In that case, a significant amount of rain can have the opposite effect and lower your pool water’s hardness levels through dilution. 


There is no chlorine in rainwater, and as you know, pool water becomes diluted by rain. Rainstorms can also fill your pool with leaves, twigs, and dust. Additionally, any runoff from your deck or yard brings even more dirt, biological matter, and other contaminants. This creates a greater need for chlorine to decontaminate your pool water, which will continue to reduce chlorine levels. Consider raising your chlorine levels preemptively if you know that a storm or heavy rain is heading your way.

What About Salt?

Salt water pools also experience dilution during heavy rains. This will require adding more salt to the pool water to restore it to the correct levels. The rain or storm may also cause the pool to need additional chlorination due to debris. 

Can Rain Cause Algae? 

Algae is very common after rainfall. While the rain itself does not cause algae, it can change the pool environment enough to make it more conducive to algae growth. Rain, storms, and runoff introduce a variety of organic contaminants into your pool. Phosphates and nitrogen are food for algae. The rain can also, as previously mentioned, alter your chlorine levels, which can make the water more hospitable to algae. This chain of events can quickly turn your pool into the perfect breeding ground for algae. Green algae is probably the most common form of algae that pool owners find, but black algae and mustard algae are also possible. 

You can be proactive and run your pump continuously during the rain and 24 hours after the rain stops. You should also perform algaecide maintenance as part of your routine pool care because it can help prevent algae development. If algae does develop, you can use an algaecide with copper to help rid it from the pool. You’ll want to brush and vacuum the pool as well. Continue monitoring your pool water to keep chemical levels balanced. 

What To Do After It Rains 

Follow the general guidelines in this pool maintenance guide and do the appropriate cleaning and pool treatment after a rainstorm. It will go a long way towards protecting your pool and your family’s health. 

1. Clean the Pool

The quicker you clean your pool after rain and storms, the easier it is to keep chemical levels maintained, and the faster you can get back to enjoying it. 

There seems to be an unwritten rule that pool water attracts an abundance of leaves and debris after rain and storms. You will want to use a quality pool rake to remove debris that has sunk to the bottom of the pool and a skimmer to remove everything that is still on the surface. A sturdy telescoping pole will allow you to reach farther into the center of the pool to get it cleaned as quickly as possible. You should also run your pump to filter out any smaller particles missed.

2. Check Your Chemical Levels

After a rainfall, you should always check your pool’s pH, total alkalinity, and calcium hardness. Your pool’s pH level should ideally be between 7.4 and 7.6, but 7.2 to 7.8 is acceptable. Your pool’s total alkalinity should fall within 100 to 150 parts per million (ppm). A healthy calcium hardness level ranges from 100-300 ppm. 

3. Check the Sanitizer Levels

The level of chlorine or sanitizer in your pool water should always be checked after rain and storms. Generally, the chlorine level should be between 1 and 4 ppm. A higher number is more reasonable if you are using a significant amount of chlorine stabilizer, but lower chlorine levels are appropriate if you are using complimentary sanitizers in your pool. You’ll want to monitor the water’s total chlorine and free chlorine as usual. If your pool’s free chlorine levels drop to zero after the rain, you may want to shock the pool. Keep your pump running for maximum water circulation, and after about six or more hours, you’ll want to recheck your pool’s chemical levels to ensure everything balances out correctly. 

4. Check Water Levels

After heavy rains, your water level may be too high. The water should be at mid-skimmer level. Turn your filter to the waste or backwash setting, and drain out excess water until it reaches the appropriate level. Another option is to use your pool vacuum to clean the pool floor and decrease your pool’s water level at the same time. 

The Next Time It Rains, Ensure You Have the Pool Equipment To Handle the Cleanup

When it rains, it pours. Make sure you’re prepared to weather the storm. For durable pool tools that will stand the test of time, ProTuff Products has you covered. Check out our pool rake special and learn how our lifetime guaranteed products mean you’ll never have to spend time or money shopping for pool tools again. Contact us today for more information about how to care for your pool and the best pool tools available. Our knowledgeable team will be happy to assist you. 

Disclaimer: Pool ownership and maintenance is very complicated, and we know every situation is unique. While we’ve done our best to cover the best practices here, we encourage you to reach out to ProTuff directly at with any specific questions you may have.

Does Rain Affect Pool Water? How to Keep a Stable Pool Environment
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