The Color of Water

The Color of Water

May 18, 2022 — The color of water can be overwhelming. As in such a marvel as to take my breath away, blow circuits in my brain, having me stunned into an almost paralysis. The top surface of the deep ocean off Molokini yesterday had a color of water that was such an undefinable shade of indigo that I had to pull myself away from staring at it from the side of the boat so I didn’t fall over when I eventually walked away. (It was also hypnotic with the up, down, and sideways motion and staring at it as intensely as I was was putting me in a trance state!) The color of water has entranced me before in emerald or turquoise pools in mountain creeks, the lambent light moving down the walls and across the floor, the gemstone edges of mountain lakes, but this oddly almost matte indigo color of the ocean’s surface off Molokini, the moving slanting breathing plates of this matte color separated by moving ridges of shine where it caught the light was like nothing else. 

The color of water as shown in a Lauren Forcella original painting
The color of water in painting, “Once Upon a Bluegreen Planet” early work by Lauren Forcella

As a former hydrogeologist, I learned about the fascinating physics of light in physics, biology and geology classes which explained why the sky and water are blue, but that knowledge (and don’t get me wrong, I’m grateful for it!) doesn’t account for the spiritual arousal the color of water (and sky) can cause in humans.

That said, I doubt the Artful Gents could speak on that spiritual metaphysical reaction, so I’ll let them explain the science on why water is blue. Well worth the read. I enjoyed the review myself.

The blue tint in water is intrinsic, caused by the selective absorption and scattering of white light. The blue wavelengths of light are scattered, analogous to blue light dispersion from the sky, but the absorption is a far greater factor than scattering in the case of transparent ocean waters. When sunlight hits the ocean, water absorbs strongly the longer-wavelength colors on the red end of the light spectrum, along with shorter-wavelength lights, including violets and ultraviolets. The oceans blue colour comes from absorption of the red and green light wavelengths by water.    Show Source Texts

In water, the absorption is stronger for red light, while it is weaker for blue, so the light of red is absorbed rapidly by the ocean, leaving it with a blue hue. When light hits the water, as with sunlight, the water filters out light, so red is absorbed while some of the blue is reflected. Experiments show that clean water — water without anything else dissolved in it — absorbed more red than blue light. According to Braun and Smirnov, the water absorbed the red light because of vibrational transformations in molecules, leaving the blue light reflecting back.    Show Source Texts

For this reason, heavier water does not absorb red light, and so larger bodies of D 2 O will not have the distinctive blue coloration of more frequently found lighter water (1H 2 O). Water absorbs more of red than of blue light. To really see the substantial difference with our eyes, the light has to go approximately thirty feet into the water. Because the absorption which gives water its colour is at the red end of the visible spectrum, one sees a blue, complementary colour of red, when looking at light which has passed several meters into the water. Some light striking the surface of oceans is reflected, but much of it enters the water, interacting with its molecules.    Show Source Texts

When sunlight hits an ocean, some light is directly reflected, but the majority of it penetrates the surface of the ocean, interacting with water molecules that encounter it. These particles in seawater bounce back part of the light before it has a chance to develop a full blue color. If there is nothing else in the water but water molecules, the short-wavelength light is likely to strike something and be scattered, making the sea look blue. This effect is magnified in an ocean, since such a high concentration of water molecules bounces the blue wavelengths back to us.    Show Source Texts

The sky is blue, not because the atmosphere is absorbing any other colors, but because the atmosphere tends to scatter shorter-wavelength light (blue) more than longer-wavelength light (red). Blue light from the sun is scattered in all directions, far more so than the other colors, which is why you will see blue wherever you look in the afternoon sky. Because the sun contains all colors, if you look down into water deeper than fifteen feet or so, it looks blue. People often wrongly assume the ocean is blue because it is reflecting the sky, but the truth is, the clearest water is only very slightly blue.    Show Source Texts

The short answer is that the ocean is blue because of how the water absorbs light, how particles in water scatter light, and because a portion of the blue light in the sky is reflected. The blueness in water is not caused by light scattering, which is what causes the sky to be blue. The blueness in water is neither caused by light scattering (which gives the sky its blue colour) nor dissolved impurities such as copper. The best answer is that the ocean is blue because it is primarily made up of water, and that water is blue in great quantities.    Show Source Texts

Basically, what makes water blue is that it absorbs light that is red, yellow, and green, and it scatters light that is blue — that is because blue light travels in shorter, smaller waves, which are easier to scatter (this is basically the same reason the sky is also blue). The ocean looks blue because red, orange, and yellow light (longer-wavelength light) is more strongly absorbed by the water than is blue light (shorter-wavelength light). At sunset and sunrise, there is a significant shift in the angle of entry of sunlight into the atmosphere, and much of the blue and green (short wavelength) light is scattered even before it gets to the lower atmosphere, which is why we see more of orange and red colors in the sky.    Show Source Texts

When light passes through water, colours of longer wavelengths are absorbed by water, the longer wavelengths being absorbed first. To get more specific, the absorption of light by water is caused by how atoms vibrate and absorb the different wavelengths of light.    Show Source Texts

Light scattered off by suspended matter is necessary so the blue light produced from water absorption can be returned to the surface and observed. Such scattering may also shift the spectrum of resulting photons towards the green, the color typically observed when observing water loaded with suspended particles.    Show Source Texts

Intrinsic colors may also be seen in snow and ice, such as the strong blue that is scattered from deep holes in new snow. Water is actually not colorless; even clean water is not colorless, but has a subtle blue color, better seen by looking through a long column of water. The slight teal colour is seen by looking through a long tube filled (or whatever) with pure water, with clear glass closing either end.    Show Source Texts

Swimming pools with white bottoms will have a transparent, rather than teal-blue, water, which is also observed in enclosed pools, which do not have sky to bounce off. In swimming pools, which for instance, contain other chemicals to make them hygienic A swimming pool, would have water that looks blue, as well, even indoors, where there is no sky to be reflected. Pure water is completely transparent, obviously — but if there is lots of water, and the water is really deep, so that there is no reflection from the bottom, then water appears as this really deep, dark, dark navy blue.    Show Source Texts

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Lauren Forcella

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About Lauren Forcella

Painting nature is my way of being devotional to this beautiful planet we’ve been born to. I strive to bring onto the canvas the livingness, aliveness, and wildness of this wonderland we call Earth… Read More

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