How Does Rain Affect Your Pool Water?

A part of living in Maryland is the spring rains and summer thunderstorms. Have you ever wondered how rain affects your swimming pool water or if there is anything specific that you should do after a rain? As a pool owner, it’s a question worth asking because, after a rain, particularly heavy rain, the water of your pool changes both on a chemical and physical level. The amount of rain is important to consider. Light rainfall and showers will not impact your pool nearly as much as a rainstorm with heavy wind.

Here are a few ways that you can expect rain to affect your water chemistry:

  • Most rainfall is acidic & will cause your water’s pH to decrease

  • This acid rainwater also reduces Total Alkalinity - Since TA is what helps stabilize and protect your pH, you can expect more significant changes in TA than pH

  • Heavy rain adds contaminants to your water including ‘runoff’ from your lawn and deck as well as sticks, leaves, and oh yeah, algae spores. Your chlorine will be working overtime, and if your pH is too low or too high chlorine is less effective.

Let’s take a look at

the top 5 things to do after heavy or prolonged rain.


    The first thing that you should do after it rains is to check your pool’s water level. Your level should be in the center of your skimmer opening. If your water is above the center of your skimmer opening, your pool needs to be drained to bring it down. Here’s what to do:

    • Set your pump to “waste” or “backwash”

    • Hook Up your backwash hose

    • Turn on the pool pump

    • Keep an eye on your water level & stop your pump once water is at the mid-skimmer level.


    Before turning on your pump, empty it and your pool skimmer baskets. Then set your pump to “FILTER.” Turn it on and leave it running while you continue with the following steps.


    It’s not time to look at your water chemistry just yet, but after heavy rainfall, for good measure shock your pool. The chlorine levels will be much lower due to fighting off contaminants. One shock treatment won’t be enough to balance your water, but it’ll work in the background as you continue to clean your pool.


    If you see anything on the surface of your pool water, skim it out now. Chances are if you wait it will end up on the bottom of your pool floor so clear out everything you can from the surface. Next, scrub the walls and stairs. If you do this right after a heavy rain, you may not notice anything, but the odds are contaminants are lurking. Then, it’s time to vacuum and clean the pool floor.


    It’s time to test your water! Test first & Then Adjust

    • Test your pH - recommended range 7.2-7.6

    • Test Total Alkalinity - recommended range from 80-120 ppm

    • Test Calcium Hardness - recommended range from 100-300 ppm

    • Test sanitizer/ chlorine levels - recommended 1.0 - 3.0 ppm

After testing, it’s time to adjust! Usually, it’s a good idea to start adjusting Total Alkalinity first (TA) first since this stabilizes your pH. After that, pH, Calcium Hardness (CH), and last but not least, Sanitizer.

It may seem like a lot to do after a rainstorm, especially considering the fact of the amount of rain we get here, but remember a light rain isn’t going to impact your pool very much. It’s the heavier rains and wind that we are addressing here. The key is to get to it right away, the more time that passes, the harder you’ll have to work and the longer it will take, and the last thing you need is for algae spores to start blooming.

Your pool is our business, so if you need us, we are here! Our service department offers storm cleanup and maintenance visits as well as expert chemical advice in our stores when you bring in a sample of water which we will test for free!

Have a question about your pool, give us a call! 301-972-3800