Should You Be Worried About Rainwater In Your Pool?



The water in your pool is filled with a delicate balance of sanitizing chemicals that make it safe for you to swim in. 

But outdoor pools are subject to nature, and a simple rainfall can upset that balance, causing problems with your pool.

A little bit of rain never hurt anyone, but you should be aware of what to do when heavy amounts of rainwater enter your pool.

Why Too Much Rainwater Can Be An Issue

A light misting or drizzle usually isn’t anything to be concerned about, but intense rainfalls can bring on the issues outlined below that will need to be rectified.

It Lowers Your pH

Pool water needs to be at a neutral pH level that’s for safe swimming. 

On the pH scale of 0 to 14, perfectly balanced pool water is between 7.2 to 7.6. Anything under this level and the water becomes acidic, anything over and it becomes alkaline.

Rainwater has a slightly acidic pH level between 5.0 and 5.5. When it combines with pollution in the air, rain becomes even more acidic, leaning into the 4.0 range.

As a result, when rain enters the pool, it’s acidity will affect the chemistry of the water, resulting in a low pH level.

Acidic pool water can cause a number of issues. Not only will swimmers experience irritated eyes and itchy skin, but pool surfaces will be stained and metals will corrode. To rebalance the water you’ll need to raise the pH level, by adding soda ash or baking soda.

It Dilutes Your Water Chemistry

The addition of large amounts of rain water will dilute your pool water, upsetting the alkalinity, which is a buffer that absorbs pH level fluctuations and keeps the water stable.

As rainwater contains no pool-related chemicals (things like calcium, cyanuric acid, and free chlorine), it won’t raise any of those levels – which is a good thing! 

However, the dilution of the water also means those chemicals will need to be re-added to the pool water.

It Raises Your Water Level

Keeping pool water circulated is vital to keeping it clean. The pool sucks in water from the main drain and the skimmers, sends it through the filtration system, and returns it to the pool via wall jets.

The level of the pool water needs to be maintained at the halfway point of your skimmer. If it drops below that level, two things will happen: 

  1. Only water from the main drain will be circulated
  2. The skimmers will take in air, which can seriously damage your filtration equipment

What causes the water to drop? Evaporation.

Pool water evaporates every single day, and some pools can lose up to 2 inches of water every week. This makes constantly refilling them a bit of a nuisance, and also an added expense to your monthly water bill.

In this sense, rain can be beneficial to help keep you pool water at the ideal level. However, you’ll still need to ensure it’s properly sanitized if a large amount of water has entered the pool.

It Can Cause Drainage Issues

Raising the water level is one thing, but too much rain can cause your pool to overflow. While your pool is equipped with drainage points, sometimes the rainfall is just too much and the overflow can lead to flooding in your backyard.

To rectify this, it’s important to have the proper drains for your pool.

Strip drains, spot drains, and french drains can all be installed to allow excess water to move away from the pool and safely off your property.

It Uses Up Your Sanitizer

The addition of rain infuses the pool water with various contaminants. This can be anything from atmospheric pollutants (phosphates, nitrates) to small organic debris around the pool like dirt and leaves

These contaminants cause your sanitizer (usually chlorine) to work harder to neutralize them, resulting in it being used up at a faster rate. In addition, a lack of chlorine will make the pool more prone to an algae bloom, making the water turn green or cloudy.

Running your pool after a heavy rainfall is recommended to keep the water as chemically balanced as possible. You may also need to add an algaecide and top up the chlorine if the situation calls for it.

What To Do Before A Storm

Paying attention to the weather can help you minimize how rainwater will affect your pool. Here’s a few tips to direct you in what to do before a storm hits.

  • Don’t drain the pool. While heavy rains risk flooding a pool, don’t be tempted to drain the pool to keep flooding to a minimum. The water in the pool is vital, weighing down the structure and keeping it in place. Heavy rains will soak your yard with an influx of groundwater, which can lead to pool popping if the pool is drained.
  • Clean up the backyard. Remove anything from the pool area that could cause damage during a torrential storm. Things like pool accessories/toys, patio furniture, and any other objects that could be blown into the pool are a hazard that need to be taken care of to keep from damaging the pool.
  • Turn equipment off. Inclement weather can be unpredictable and devastating. Make sure you turn off your electrical equipment during the storm as damage to it can be catastrophic.
  • Test & balance the water. By testing and balancing the water beforehand, you’ll be on top of it so that you’ll have to do minimal maintenance on the pool water after the storm is over. Adding chlorine and algaecide can keep the pool water from being overly contaminated during the downpour.
  • Prep for extreme weather. Heavy rain storms can also wreak havoc on the exposed parts of your pool. If you have a traditional pool cover or solar cover, we’d recommend rolling it up on its reel and securing it, and if your pump is outside, disconnecting it and covering it with a tarp is also good safety practice. The last thing you want to do is have to buy new equipment because of some rain!

What To Do After A Storm

Follow these steps to restore your pool after it’s been subjected to heavy rainfall.

  • Pump water from your cover. If you happened to have a cover on your pool when the rain struck, you may have a pool of water (excuse the pun) sitting on the cover. It’s best to use a pool cover pump to remove this before removing the cover.
  • Check the water level. After a massive downpour, you’re most likely going to have too much water in the pool. By backwashing using your pool filter, you can pump out the excess water in a matter of minutes. This entails attaching a hose to the filter, and running it on the “backwash” or “waste” setting. Once the water level is reduced to the halfway point of the skimmer, you’re in good shape again.
  • Turn on your system. Clean out your skimmer basket, set the pump back to “filter” mode, and begin circulating the water again.
  • Shock the pool. Due to the amount of contaminants and dilution that occurs during intense rainfall, shocking the pool is a good idea to kill off all the bad things in the water.
  • Clean the pool. Break out the skimmer net, vacuum (or auto vac), and pool brush! A thorough cleaning will be needed, so make sure you get into every nook and cranny. Also don’t forget to give your drains a hand by cleaning the pool deck.
  • Test the water & add chemicals. Rebalance the pool water by using a testing kit to find out where the pH, alkalinity, calcium, and free chlorine levels are at, and top up the water with the necessary amounts to bring the pool water back to a neutral state.

Rain, Rain, Go Away!

Rainfall is a natural cleanser, but rainwater in a pool can be troublesome at times. 

Light rain exposure shouldn’t be much of an issue, but during heavy rainfall you should know the precautions and treatment steps needed to keep your pool functioning at its optimal level.

Categories: Pool Care, Pool Problems