what does rain water do to a pool

What does rain water do to a pool? Quite naturally, people want to cover their pools when it is raining, but why is that?

Millions of people all around the world use their swimming pools as a way to unwind and have fun. However, it can be difficult to keep a pool’s chemicals and water quality in check.

Rainwater is a potential pool water quality issue that is often disregarded.

But, what does rain do to pool water and why is it important to take measures to keep rainwater away?

Rainwater can alter the pH of a swimming pool, add contaminants to the water, damage the pool surfaces, and irritate swimmers. 

What Does Rain Water Do to a Pool?

rainwater on pool effects

When talking about the impact of rainwater on swimming pools, the dilatation of chemicals seems to be the biggest issue. Though it is not!

Precipitation can indeed have a negative impact on pool water, however contrary to popular belief, the ‘dilution’ of pool chemicals is not to blame for the issues precipitation can create.

Dilution is typically not an issue when adding an inch of rainwater to a normal 50,000-liter pool because the increase in water volume is only approximately 1.5%.

What matters more is what the rain brings into the pool. Algae spores, which float around in the air, find their way into bodies of water after a rainstorm.

Rain washes these spores and everything else floating in the air over a pool down into the water below. 

Several Ways Rainwater Affects Your Swimming Pool

several ways rainwater affects your swimming pool

Depending on how hard it rains, any rainwater finding its way into your swimming pool can cause various problems.

For instance: 

Dilution of Chemicals

As mentioned already, light rain is less likely to dilute chemicals in your swimming pool, but it is a different story in the case of a rainstorm.

The depletion of chemical concentrations is always an effect of precipitation on swimming pools.

Rainwater washing into a swimming pool can dilute the concentrations of necessary chemicals like chlorine, pH adjusters, and stabilizers, threatening the pool’s safety and cleanliness.

algae growth

This can lead to a chemical imbalance, which can cause difficulties including:

  • Inefficient sanitation
  • Algae growth
  • Health Problems for swimmers

To keep the chemical levels in swimming pools at the appropriate level for swimmer safety and comfort, pool owners must be constantly vigilant, especially after heavy rains. 


Rainwater can significantly alter the quality of swimming pool water by bringing in debris, dirt, and pollutants from the surroundings.

These impurities can raise the pool’s organic matter, which algae and bacteria can use as nourishment.

Cloudy and discolored pool water poses a health risk to swimmers.

Fact: Regular skimming of the surface, vacuuming of the floor, and adequate chemical levels are all things pool owners can do to lessen the impact of these contaminants. 

Impact on pH Levels

impact on ph levels

The somewhat acidic character of rainwater, with a pH level between 5.0 and 5.5, can have a major impact on the pH balance of pool water.

A decrease in pH due to precipitation entering the pool can have serious effects on the pool’s infrastructure and the swimmers who use it.

To avoid these problems and guarantee a pleasant, healthy, and stress-free swim, it is essential to keep the pool’s pH level between 7.2 and 7.6

What Does Rain Water Do to the pH of a Swimming Pool?

swimming pool ph due to rainwater

One of the biggest issues rainwater causes is by changing the pH of swimming pools.

It can affect your swimming pool in many ways, including:

  • Corrosion
  • Damage to pool surfaces
  • Irritation for swimmers
  • Ineffective sanitization 


Swimming pool metal components are susceptible to corrosion when exposed to acidic pool water, which is water with a low pH.

Acidic water can corrode important pool infrastructure including:

  • Ladders
  • Handrails
  • Metallic components of the filtration system

Corrosion can eat away at the metal, eventually causing it to fail in its intended function.

Thus, potential safety problems may emerge, endangering swimmers and necessitating expensive repairs for pool owners.

Preventing these problems requires keeping the pool’s pH level stable, which is important for the longevity of the pool’s components and swimmer safety. 

Damage to Pool Surfaces

damage to pool surfaces

When the pH goes down and your pool water becomes more acidic in nature, it can damage pool surfaces.

Low pH levels can be extremely damaging to certain pool materials, including:

  • Plaster
  • Vinyl
  • Fiberglass

Chemical reactions triggered by acidic water can etch and degrade these materials, threatening their durability and aesthetic appeal.

This can shorten the lifespan of pool surfaces and make them look harsh, discolored, and unsightly. 

An Important Consideration

Keeping the pH level within safe limits is crucial for avoiding this kind of damage.

This will help keep the pool’s inner surfaces in good condition, extending the life of the pool and making it more pleasant to swim in.

Fact: The use of a pool cover and careful management of landscaping and drainage can reduce the likelihood of contaminants entering the pool during wet weather. 

Irritation for Swimmers

irritation for swimmers

Due to the acidic nature of the water, swimmers may feel a variety of irritations if the pH level in the pool is too low.

Eye irritation can produce redness, burning, and grittiness in the eyes, while skin irritation can present as itching, redness, or dryness. 

Additionally, those who are particularly sensitive may experience coughing or difficulty breathing as a result of respiratory irritation.

Keeping the pool’s pH within a safe and comfortable range is crucial for the well-being of everyone who uses it.

Preventing these problems and making swimming more pleasant for everyone requires regular monitoring and adjusting pool water chemistry. 

Ineffective Sanitization

ineffective sanitization

When pool water pH is too low, chlorine loses some of its disinfecting power.

This can lead to a decline in water quality and an unsightly and perhaps unhealthy environment for swimmers due to the proliferation of germs and algae.

Infections of the skin, eyes, or stomach are just some of the potential issues you face with chlorine losing its sanitizing power.

To preserve the health of their swimmers, pool owners should frequently check and adjust pH chlorine levels.

This will ensure that the sanitizing chemicals are doing their job.

Fact: When the pH is too high, however, it is necessary to utilize pH reducers such as muriatic acid or sodium bisulfate. 

Managing the Impact of Rainwater on Swimming Pools

managing impact of rainwater on swimming pools

Several methods can help pool owners reduce the negative impacts of precipitation and keep their pools at the ideal pH level.

For instance: 

Regular Checking

Regular water chemistry testing is essential for detecting shifts in pH and other chemical levels in a swimming pool.

When there is a lot of rain or a lot of people using the pool, pool owners should check the water quality more often. 

Adjusting pH Levels

adjusting ph levels

If a swimming pool’s pH level is determined to be too low, pool owners can employ pH increasers like soda ash or sodium bicarbonate to bring it back into the ideal range. 

Check Chlorine Levels

 Chlorine is the most important sanitizer.

Regular testing and adjusting sanitizer levels, especially after significant rainfall, is necessary maintenance for swimming pool owners.

Fact: A swimming pool's chlorine concentration should ideally range from 1 to 3 ppm. 

Keep the Pool Covered

keep the pool covered

Precipitation can have a negative influence on the pH levels and overall water quality of a swimming pool.

Still, a pool cover can help prevent precipitation and debris from entering the pool.

When the pool is not in use for long periods of time or during periods of heavy rain, pool owners should think about using a cover. 

Removing Debris

Cleaning up after rain is as simple as skimming the surface and vacuuming the floor of the pool on a regular basis.

Keeping the pool’s surroundings clean will not only improve the quality of the water, but will also reduce the possibility of algae growth and other problems

Balancing total alkalinity

balancing total alkalinity

The total alkalinity (TA) of water is a measurement of its buffering capacity against variations in pH.

When precipitation hits the pool, the pH level can fluctuate significantly; keeping the TA level stable can help mitigate this effect.

Fact: Keeping the total alkalinity between 80 and 120 ppm can help improve the water quality of your swimming pool.


What does rain water do to a pool? Rainwater is acidic in nature and it can have a direct impact on the pH of your swimming pool.

This change in pH can have a direct impact on the sanitization and integrity of your swimming pool.

Be sure to check the pH and chlorine levels of your swimming pool after a rainstorm to ensure everything is in perfect balance.