Crystal clear, sparkling blue water. That’s what makes swimming pools inviting, that’s what we’re all striving for. But what exactly makes a pool, or of that matter, any other large body of water appear blue?

In a swimming pool, usually it’s the result of the water being clear and free of algae, combined with a blue pool surface such as a blue tinted liner, blue painted gunite, etc.

But what makes the bottomless ocean or clear mountain lake appear blue on a sunny day?  The answer lies in some simple physics. Foremost is the concept of reflection.

When we look at a body of water on a clear day, most often what we are actually seeing is the reflection of the blue sky bouncing off the water’s surface.  This is why we commonly associate water with the color blue.

But, if a water surface only looks blue because its reflecting the blue sky, then is water itself colorless? If not, then what is the actual true color of water?

For the most part, water is transparent to just about all the visible frequencies of light and therefore almost colorless.  This is why a swimming pool tends to take on the color of it’s liner or painted bottom.  However, water will absorb infrared waves. Which incidentally, is why the water is warmed by the sun. While this is happening, the water also absorbs a small amount of visible red light.

As the water absorbs red light, it simultaneously reflects back all the remaining colors of the spectrum. These remaining colors mixed together become cyan — a greenish blue.  Since the color of water, or anything else, depends on what colors it reflects and what colors it absorbs, the true color of clean, clear water is cyan.

You can see this for yourself by placing something white into a clean body of water and looking closely.

Unfortunately, not all swimming pool water appears blue or even greenish blue.  In order to have the proper reflective qualities the water must be clean, free of algae, and other suspended particles. Otherwise a swimming pool will appear murky, cloudy or just plain green.

In brief, the “blue” swimming pool water that we all enjoy is the product of good chemistry, some simple physics, and a lot of summer sunshine.

The laws of physics don’t change. Therefore, like the weather, they’re something none of us can do anything about.  But the chemistry of your pool can be accurately controlled.  By bringing your pool water to Galati Pools & Spas for a complete analyze, you’ll be able to maintain it’s correct balance and keep those summertime blues shimmering.