How Does Rain Affect My Pool Water?

Publication date : Monday, April 11th, 2016

Rainwater has acidic properties that can affect the water in your swimming pool. This happens because rainwater absorbs industrial gases in the atmosphere. So what do you do if the weather is calling for rain?

A little bit of rainwater shouldn’t do much damage. A heavy rainfall can. Let’s learn a bit more about why rainwater can affect your pool water.

Why Does Rain Make a Difference?

Rainwater has a naturally lower pH than what you keep your pool at. Most swimming pools are kept around 7.4 to 7.6. Rainwater, on the other hand, has a pH of around 5.0. If enough rain falls into the pool, it can lower the pH levels.

The reason why pools are kept at a higher pH is because the human eye has a pH of 7.5. Fluctuations in the pH can lead to serious discomfort such as burning. That’s why you sometimes hear people complaining of their eyes burning when they swim. This isn’t the chlorine causing the burning, but the pH level.

Do I Have to Adjust My pH Every Time it Rains?

If there is a light rainfall, you shouldn’t have to adjust the pH level. While the rainwater may lower the pH level right after it rains, this shouldn’t be for long. If you do a good job of maintaining the proper chemistry of your pool water, you really shouldn’t have anything to worry about.

If there is a big rainstorm, however, you will have to adjust the pH level. The best way to do this is by draining a bit of the water and re-testing the chemicals.

What About Runoff?

Another factor to consider is rainwater that comes off your landscape or deck and then runs into your pool. Not only does the water contain a lowered pH, but also it contains other runoff elements that can change the calcium, hardness, alkalinity and total dissolved solids in your pool. Plus, things like dirt and debris can bring contaminants into the water and cause damage to some of the pool parts.

Can Rain Ever be a Good Thing?

In some instances, rain can be beneficial. There are certain chemicals (calcium, stabilizer) in the pool water that cannot be lowered without diluting the water, which rainfall can help with.
In general, as long as you take care of your pool on a regular basis, you shouldn’t face any issues after a standard rainfall. If the weather is calling for a severe storm or several inches of rain, stay ahead of the game by testing pH levels.