Why My Pool Water Turns Green After Heavy Rain? [Updated!]

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When it rains, your pool water quickly becomes cloudy, right? After all, water is water, but the color of liquid varies from light to dark reflecting the amount of impurities present in it. Well, you’re definitely not alone in thinking this way. However, did you know that the color of your pool water is not necessarily an indication of what’s in it? While it’s true that most of the time the water in your pool is the color of glass, this does not mean that it is necessarily safe to drink. The truth is that your pool water could be contaminated with algae and other unsafe substances.

So, what exactly causes the color of your pool water to turn green? It’s not due to any single factor, but a combination of several factors including temperature, sunlight, and chemical reactions. In this article, we’re going to discuss what exactly makes your pool water turn green after heavy rain, so you can better understand what’s going on and how to fix it. If you want to learn more, continue reading.


In most cases, when it rains heavily, the temperature of the air rises, causing the temperature of the water in your pool to rise as well. As the water gets hotter, the tendency is for it to become less transparent due to the increase in light scattering (the way light is scattered when it passes through a liquid is called “cloudiness”). As the light scattering becomes more of a problem, the color becomes more of a problem as well. Because of this, if you live in a warmer climate with warm rain, you’re likely to experience problems with your pool water due to the increase in temperature.

Chemical Reactions

When it rains, chemical reactions happen as well. The process by which chemicals in water change state or form is called “chemical reaction.” These reactions can change the chemicals entirely or they can change the state of the chemicals, making them behave differently. There’s a wide range of chemicals present in your pool water, and while some of them are essential for life, most of them are not. In these cases, heavy rain can cause some of the chemicals in your pool to undergo reactions with other chemicals or elements present in the water, giving your pool water an undesirable taste and making it discolored as well. Some of the chemicals that can undergo reactions include chlorine, ammonia, and bromine, which can change the color of your pool water to a greenish tint.


Algae is a type of plant that grows rapidly when exposed to sunlight and high temperatures. Due to this, whenever there is an abundance of sunlight and heat, you’re going to see algae grow rapidly. This is why algae blooms happen during warm months when the sun is directly overhead. The intense light and heat promote the growth of algae, quickly turning the pool water a cloudy, greenish tint. While swimming pools themselves are not harmful, algae in large quantities can produce a slimy, unpleasant feeling when in contact with your skin. If the concentration of algae in your pool reaches an unsafe level, it could pose a threat to your health.

Protection From Sunlight

Did you know that sunlight is dangerous for your pool water? While it’s true that sunlight is essential for plant life and helps to make vitamin D, it also causes several problems to your pool. The most significant problem caused by sunlight is photodilation, in which the light energy contained in sunlight is converted into energy the algae can use. As a result, the algae grow rapidly when exposed to sunlight, quickly turning your lovely pool a nasty shade of green. The photodilation process causes several other problems as well including the destruction of vitamin D, which is required for the human body to function properly. While algae does serve an important purpose in your pool, it also causes problems that could potentially be harmful to your health. To prevent this, cover your pool with some type of cover whenever possible to protect it from direct sunlight. If this is not possible, then use a pool filter to ensure solid connections between the water and the vacuum pump to prevent dirt from being sucked into the water along with the drinking water. This will help maintain that fresh pool feel all year long!

Why Does My Pool Water Turn Green After A Few Days Of Sunset?

As mentioned above, whenever there is an abundance of sunlight and heat, you’re going to see algae grow rapidly. However, not all algae is created equal. There are several species of algae that grow and reproduce faster than others, turning your pool water a nasty shade of green quickly. This is because when algae reach a certain size, they can become a food source for small fish and other aquatic animals. While this is typically a good thing, if the concentration of algae becomes too high, then it could become a threat to your health. To save yourself from any potential algae problems, cover your pool with some type of cover whenever possible, and clean it regularly with chlorine and other chemicals to promote healthy growth of marine life.

The Final Word

While most of the time your pool water is clear and looks lovely, it’s important to keep in mind that it could be contaminated with algae. Whenever you experience heavy rain or the sun is directly overhead, you’re likely to see algae bloom rapidly due to the increase in heat and light. To avoid any health problems due to algae, it’s essential that you keep your pool clean by swimming in it at least once a day and cleaning it regularly with chemicals and water changes. If you want to learn more, then check out our blog post on how to maintain a beautiful pool and keep it smelling great all year long!

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