Does Rain Lower Pool Alkalinity

For some pool owners, a serious rainstorm can contain acid and other chemicals that can turn your swimming pool nasty, cloudy or green, yet with other pools, it won’t matter at all. You can’t stop Mother Nature and heavy a rainstorm but you need to know how to prevent pool problems before they happen. Does rain lower pool alkalinity?

Taking a defensive approach, a pool owner can ward off the effects of acid rain, that lowers alkalinity and pH even in a well-balanced pool before it rains by:

Increasing the pool water Alkalinity levels up 20-30 ppm
Raising pH up to 7.6-7.8 range
Bumping Chlorine Residual up
Running  Pool Filter more

The way to defend your swimming pool from the effects of Acid Rain and other nasty elements that happened during a summer storm is to prepare your pool especially the water’s chemistry before it even happens. Buffering capacity is strong enough that it will keep your pool water bouncing back and ready to go.

What’s in Rainwater

Acid rain sometimes referred to as acid deposition, is a broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.  This can include rain, snow, fog, hail, or even dust that is acidic.

Acid rain can occur when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and moved around in the wind and air currents. These component chemicals end up mixing and reacting together with water oxygen other types of chemical gases and eventually end up falling back to the ground. Other types of components like ammonium, carbon, nitrogen, and sulfur are also released into the atmosphere. The wind and air currents carry the gases high into the sky.

The sources of sulfur dioxide (SO2) and nitrogen oxides (NOX) that are found in the earth atmosphere come from:

  • Burning of fossil fuels to generate electricity.  Two-thirds of SO2 and one-fourth of NOX in the atmosphere come from electric power generators.
  • Vehicles and heavy equipment.
  • Manufacturing, oil refineries, and other industries.
  • Naturally, as it would from an active volcano

Wind and air currents can blow the chemical mix for miles into surrounding areas so the Acid Rain formed doesn’t stay in the proximity of where the source is located. Sunlight can also act as a catalyst to increase the rates of these chemical reactions. Nitrogen oxides can be produced naturally by lightning strikes and sulfur dioxides are formed when volcanoes explode, but acid rain can also be caused by emissions due to humans.


Cloudy Pool After Rain

As a Pool Owner you know that the most important part of the upkeep of a swimming pool whether it’s an Above ground in-ground small pool or big pool, Saltwater or Freshwater is the chemistry that the pool water relies on for the chemical you put in to do their job. If the chemistry isn’t right the pool water won’t be right. You have heard this a hundred times. Whenever you talk to a new pool owner the subject of rain always comes up as an automatic excuse or that their pool will be messed up cloudy or even green and there won’t be anything they can do about it. Darn rain!

Think about it, if you ever spent time at a neighbor’s house who is having a barbecue or a backyard picnic and they have a pool if there is the slightest thing wrong with the pool they will blame it on the rain.

The problem with your pool is not the rain it’s you. Sure rain makes for a good reason to tell the neighbors or the friends that come over for the weekend party but the reason it rained and the pool turned cloudy or even green is because you didn’t do something or enough of something preparing to measure or taking some extra steps to ensure your pool was ready for it. As you can see from this map of the US, rainwater is known to have acidic properties that can negatively affect your pool water chemistry balance.

This can affect anything from the pH balance to alkalinity levels and more. The pH of rain across the US, which includes acid rain, is due to industrial gasses that make nitric and sulfuric acid. This will affect the pH and alkalinity calcium hardness that all depends on how much rain you get. A storm can add debris like tree branches, twigs, leaves, and grass that can add phosphorus and organics nutrients that will affect chlorine residual it pushes phosphorus levels up

Besides the damage that Acid Rain may do to your swimming pool if unchecked at the source, Acid rain increases the acidity of soil which is not good for plants. Acid rain in streams, lakes, and rivers causes damage to many fish species and they cant survive. Trees are destroyed by acid rain.

Fish are also killed by acid rain. Acid rain dissolves the material of statues and historical sculptures and is destructive to other buildings and infrastructures that we depend on every day that is unseen for many years until it’s too late to be repaired. Your swimming pool is a small example that should be maintained and protected just by providing a daily maintenance plan. So read on.


Protecting Your Pool Before It Rains

The best defense for your swimming pool against Acid Rain is to build a wall or block between the pool water’s chemistry from the dilution of rainwater that can happen during a heavy rainstorm. Most regions in the US are slightly acetic so there will be a known effect the longer and heavier it rains. As always I urge pool owners to bring up the alkalinity before it rains. Give it some muscle!

If you are in a are part of the country where there are known problems with acidity in the rainwater. The higher alkalinity is a Bulletproof Jacket that will prevent the pH from slipping and dissipating even when it’s being attacked by carbons, sulfur dioxide (SO2) and nitrogen oxides (NOX) that act as acids lowering the pH of your pool water.

A chemical reaction happens when sulfur dioxide and nitrogen oxides mix with water, oxygen, and other chemicals in the air. They then become sulfuric and nitric acids that mix with precipitation and fall to the ground.

Precipitation is considered acidic when its pH level is about 5.2 or below. The normal pH of rain is around 5.6 but is averaged according to what the rain is around the country. In the Northeastern part of the US, it can get much lower. Before a known summer storm:

In Nature- Because of the pH of rain and it’s acidic nature, it can destroy the environment around that area where the rain falls. The ground trees and the environment is able (in most cases) to survive by adjusting the low pH of the rainfall because the soil has the capacity to buffer the acid rain that’s flowing through it. Some regions like the Northeaster part of the country become vulnerable and lose that capacity. Years of industrial production and population help weaken and add to it.

In your Swimming Pool, you are doing basically the same thing. The chemistry in your swimming pool is dependent on the capacity of the water to be able to buffer the sudden changes so that the sanitizer can continue to do its job. Even though the Process in Nature works biologically and the process in your pool works chemically.

Swimming Pool After Rain

Use your common sense- first after a storm:

  • Clean debris- branches, leaves, dirt, and any organic material that will only soak any chemicals that you add to the pool to correct the chemistry.
  • Use the basket bag skimmer for cleaning large material from the bottom
  • Skim the top of the water
  • Clean outside the pool area that has blown near the vicinity of the water
  • Get the filter running
  • Lower the water level while you vacuuming
  • Check the Alkalinity first and see how you held after bumping it up
  • Adjust pH
  • Shock with Chlorine


During a big storm, you may want to use your winter pool cover to keep the trash and debris that is going to end up in your swimming pool. To me it’s more work then it’s worth but you could be dealing with storms that are not ordinary and want to get the protection only a winter pool cover can give you.

There is a fairly new product that looks like a pool cover that is a mesh type material that goes over your inground or above-ground pool called SMOPS Leaf Net Cover for 12-Foot-by-24-Foot Rectangle In-Ground or Above-Ground Swimming Pools | Keeps Leaves and Other Debris Off Your Winter Pool Cover found on Amazon

It is a large net mesh cover that will cover the pool cover in the winter but you can also stretch it over your pool and catch leaves and trash that will blow into the pool during a storm – I checked it out it folds up nicely and is light enough to put on and take off with 2 people. It may be worth the price!



JimGalloway Author/Editor



EPA-Acid Rain Program Historical Reports


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