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What Turns Pool Water Blue?

When it comes to above-ground and in-ground pools, there are a lot of frequently asked questions about pool health and upkeep. But did you know that one of the most common questions about pools is, “Why are pools blue?”  There are many myths regarding what turns pool water blue.  Let’s look at a few of these myths and get to the bottom of the pool color mystery.

Can you tell the truth from the lies?

Some Popular Myths (and one truth)

  • The sky makes pool water look blue.
  • Pools are painted blue at the bottom.
  • Swimming pool chemicals turn the water blue.
  • Water turns light blue.
  • It’s a mystery! No one knows.

Pools are Painted Blue

All pools are painted blue to give them that crisp, blue feeling. Just add water! It’s a combination of paint and pool psychology!


Not all pools are painted blue at the bottom.  The most common pool finishes include white, blue, and a combination of both. However, due to developments in pool technology, more natural and unique pool finishes have experienced a meteoric rise in popularity. In fact, some of the more popular choices today include simulated stone, glass and porcelain.

And guess what … in most cases, the water still looks blue.

Pool Chemicals Turn Pool Water Blue

Pool water is dyed blue by the chemicals used to keep it healthy.


Chlorine is added to pools to keep the water clear. It is not a dyeing agent. Even though we may think a healthy pool is a blue pool; a healthy pool is actually a clear pool. It’s also important to point out that salt water pools, which use salt chlorine generators are just as healthy and just as clear as those using traditional chlorine.

And guess what … in most cases, the water still looks blue.

Blue Skies Make Blue Pools

The sky is blue. Water is reflective. So, logically, swimming pools are blue because they reflect the color of the sky.


The blue color of the sky has little to do with the color of water. Have you ever seen a glass of water turn blue because it is outside? Are indoor pools any less blue than their outdoor counterparts?

It’s a Deep Blue Mystery

Perhaps this was all just a trick. There is no answer. No one knows why pool water appears blue.


Don’t give up hope! There is a reason why pool water appears blue.

It’s just a matter of how…

pool water, blue pool, girl in pool water, sun behind pool water

Water Turns Light Blue

According to Dr. Paul Coxon, in a CNN.com article titled Why are swimming pools usually blue, the molecules of water absorb red light and reflect blue light.  “You notice the blue effect when you have a large volume of water because of the way molecules are slightly absorbing light from the red end of the spectrum,” Coxon says. The deeper the water, the more blue it appears. He also points out that the same thing happens under artificial light.

Bringing it all Together

What’s interesting about this deep blue mystery is the fact that each myth has a bit of truth. Pool finishes are often designed to enhance the blue coloring of water; chlorine keeps water clear, which allows the light to absorb and reflect as it should; and the sky casts light, which is absorbed and reflected by our pools’ water.  Whatever the reason, nothing compares to the refreshing sensation of diving into the crystal blue water of your very own pool.