While not often considered by pool owners, rain water can seriously affect your pool. In this article we will review the various ways that rain water can affect your pool, and give you our recommendations for how to combat these effects.

Water Balance

The biggest way that rain will affect your pool water is in its effect on water balance. Pool water is balanced to ensure three things:

1. It is comfortable for you to swim in. pH is designed to match the pH of your eyes to prevent redness and irritation.
2. It is safe to use. Chlorine is added to kill bacteria and other microorganisms that can cause a variety of issues in your pool.
3. Your pool equipment is safe. Calcium hardness and common metals like copper and iron are balanced to prevent issues with staining on the liner and scaling of the pool’s plumbing and equipment.

Rain water is not balanced with any of these things in mind. It is typically on the acidic side of the pH scale, does not have any sanitizing properties and the calcium hardness / metal levels can vary drastically depending on your region. The more it rains, the more the balance of your pool water will change.

What Can You Do?

We recommend that you check your water balance with a home test kit after any big rainfalls. You will likely need to make some small adjustments to bring everything back into balance. If larger changes look to be needed, we recommend bringing a water sample in to get a free professional water test.

Diluting Your Chemicals

Not all chemicals in your pool are designed to balance the water. Three critical chemicals that don’t affect the balance of your pool water are:

1. Stabilizer. The UV radiation of the Sun can quickly break down chlorine in your pool water. This forces you to use more chlorine to keep your pool clear of bacteria and can cause issues with cloudy or green water. Stabilizer greatly increases your chlorine’s resiliency to UV radiation; meaning that you’ll need much less chlorine to maintain a clean, clear pool.
2. Algaecide. Algaecide helps to break down the protective layers of slime that bacteria cover themselves with. Once this protective layer has been removed, the chlorine in your water is able to kill the bacteria much more easily. This leaves more chlorine available to kill bacteria; ensuring that your water stays clean and clear with less chlorine needed.
3. Stain & Scale Control. For those that struggle with high calcium hardness or high levels of metals like copper or iron; these chemicals are essential in preventing metal staining on your liner and scale from forming on essential components of your pool like the pump impeller and the heating element.

It will come as no shock that rain water does not contain any of these chemicals. The more it rains, therefore, the more these chemicals are diluted in your pool water. While you will typically add algaecide and anti-scaling chemicals on a fairly regular basis, the same is not true of stabilizers.

What Can You Do?

If you notice that you’re going through more chlorine than is normal for your pool, the answer could be a lack of stabilizer caused by dilution from rain / evaporation. Take a sample of your water in for a professional test to check the stabilizer levels in your pool and add more as needed.

Changing The Water Level

Rain storms add more water to your pool, though this additional water is usually balanced off by the water lost from evaporation. If you get a particularly large amount of rain, however, you can end up with water levels in your pool rising past where they should.

Pools filtration systems are designed around a specific water level (with the water covering between 1/2 and 2/3 of the skimmer. If the water level is higher than this, the skimmer will struggle to create enough suction to properly skim the surface of the pool. This means two things:

1. There will be more organic debris like leaves left in the pool water.
2. Less water will pass though the filtration system.

Both of these issues will lead to more algae growth in the pool; causing the water easily turn cloudy or green. For this reason we recommend checking the water levels in your pool after larger than average rainfalls.

What Can You Do?

If the water level in your pool is too high, simply set your pool filter to “waste” and remove water from the pool until you reach the recommended water level.

Bringing Other Contaminants Into The Water

Along with rain itself, rain storms often bring wind that can knock leaves and other plant matter into your pool. They can also wash dirt and other debris from the ground into the water. These contaminants add phosphates to the pool water; which act as food for algae. The more phosphates your pool water has, the easier it is for algae to grow. Pair that with the dilution of your sanitizing / stabilizing chemicals and you have a recipe for a green pool!

What Can You Do?

If you notice debris floating in your pool or sitting on the bottom of the liner, we recommend skimming and vacuuming the pool to remove as much of that debris from the pool as you possibly can.

Wrapping Up

Rain water plays a lot larger of a role in the overall health of a pool than many pool owners realize. This doesn’t mean that you need to run out and do a bunch of work every time it rains, however. A little bit of testing and some minor adjustments should be all that is needed to keep your pool looking great after any rainstorm!