What color is water?

What color is water?

You fill a bottle up with water and look at it and the answer is evident- water is colorless, right? But that’s not quite correct.

So then what color is water?

It will come as a happy coincidence to you that as child you were right to reach for that blue crayon to color the ocean in your painting- because water is in fact blue in color!

But aren’t oceans blue because the water reflects the color of the sky?

That is a pretty good argument, but a light blue hue is an intrinsic property of water. There is actually a solid scientific reason behind this- the blue color is caused because water absorbs the longer, redder wavelengths of light, while leaving the bluer wavelengths unscathed. This gives water its blue hue.

You can prove this by doing the following experiment:

Shine a white light through a long column of pure water, the liquid will look faintly blue.

So then why does the water in your bottle look colorless?

The absorption of red light by water is only apparent when the thickness of water exceeds 1 meter. This is why your bottle of water appears colorless.

Then why don’t all water bodies appear blue?

Despite all this evidence, water does appear to be different colors in real life. Like a local pond can be a murky green and by contrast swimming pools can look unnaturally blue.

 These changes happen because the constituents in water can significantly alter its color. For example algae in a pond can change the affect the color of water and make it look green. Similarly a pigment released from decaying matter, known as Tannins, can make a water body look tea brown and murky. The water in a swimming pool however is treated with chemicals so the water is cleaner and therefore it appears bluer in hue- even indoors, where there is no sky to be reflected.

So in practice, the color of water is split into two categories:

Apparent color which the color of water as we see in real life and Real color which is what we see when water has been filtered and purified.