2 July 2011

The Color of Water

What color is water? It is a question that many children ask, not to mention adults, and the answer is invariably that it has no color. It is transparent, clear, see through. Is that answer the correct one?

Take a look at that lovely cool wine glass of water above. Looks refreshing and thirst quenching, yes? No? Let me take a look. Oh dear! Well, disregard the goldfish if you can but the water is colorless, right? Wrong. The water does have color but it is not something that the human eye can see when H2O is present in such small quantities.

In order to see the real color of water we must take a look at a large body. By large body, we do not mean Arnold Schwarzenegger, but a place where a great volume of water can be looked through or down into. It can be done scientifically as well, but the human eye can see the intrinsic color of water in the right conditions. You may well have already guessed what that color may be.

Well yes, okay. It is blue, light blue –some would even argue turquoise. Now before you close this page, spare a second to think about why you thought that. Is it because you think that it is due to the reflection of the sky on the surface of a large body of water, such as the sea? So, when the day is overcast and cloudy, how is it that the sea then appears to be the same color or perhaps an even darker blue than on bright, cloudless sunny days? True, the reflection of light does contribute to the color that the water looks, but only when the surface of the water is very still. The picture below, taken at Los Cabos, Mexico shows the sea at its stillest and most serene – and as such its bluest. The red you can see is pure reflection, however, not the color of water at all.

The amount of this color caused by reflection is due mostly to the angle at which you look at it, which in scientific terms is known as the angle of incidence. Put simply it is how many degrees away from looking at water straight on that you are. The higher the angle, the bluer the water will appear due to reflection. This is because the reflectivity of the water is higher in direct correspondence of the angle of incidence. Water can quickly become totally reflective under these conditions.

Of course, what is in the water plays a very important role in the color we perceive it to be. These salt ponds in the US are full of algae. Pink algae. It is not, as legend has it, that the water has such a low PH that when flamingoes attempted to land there that they were effectively melted. It is due to the presence – in very large quantities – of the microalgae Dunaliella salina. So, what more proof can there be that what is in the water often predetermines the color that we see?

Algae is usually associated with the color of green and that of course will change the color of the water. It can also be done by human hand, of course. The denizens of Chicago often turn the color of their river green on Saint Patrick’s Day. Quite what it does to the fish in there – if indeed there are any – is anyone’s guess.

The magnificence of the deep blue of the sea off Montserrat (picture above). .A lot of the color you see comes from the depth of the water, not the sunlight cascading down upon it. White sunlight contains all the colors in the spectrum. Water gives absorbing all these colors a good go but some of them are absorbed more than others. It is only, in addition, any good at doing this if it has a lot of company. In other words, cup sea water in your hands and it appears clear, throw it back in the sea and it joins the rest of the countless H2O molecules in there to become blue.

The sea’s water can absorb red light very well, and so the sea is not red. However, the water does not absorb blue light very well and so this light is transmitted through the water. As it is not absorbed, you perceive the water to be blue. Yes, it is absolutely the same principle as to why the sky is blue as well. We can be blinded by science as well as the sights!

The ferries coming in to the Maldives (above) are dwarfed by the sea and its magnificent multi-coloring. If you have ever been in a swimming pool which has had its sides and bottom white washed you will have noticed that the water appears turquoise. This is even inside when there is no light to be reflected. So it is in the outside world – the true color of water is best seen from above. This beautiful shot from Minorca, below, illustrates this wonderfully.

In terms of the visible spectrum, red and blue are complementary colors. So it is the blue that we see as we observe light passing through water to greater depths. The lower we go, the bluer it seems to get. When flashlights are used by divers then the ‘real’ colors emerge but anything at a distance of more than a few feet appears blue – even though it isn’t really.

This color can be seen in deep snow and ice as the color scatters back. Likewise when a waterfall is frozen you can often perceive the water to be almost of a bluegreen hue as these colors are scattered back because of the deep penetration of light.

The color that we perceive can also be governed by what is in the water itself. Have you ever gazed at the sea, musing on life’s imponderables (that sounds like an oxymoron)? You may well have noticed that different parts of the sea are – or seem to be – different colors. This lovely shot from the Maldives clearly shows the sea as different colors. It can be caused by the presence of clouds and their associated shadow, but often it seems not to be the case (especially, of course on cloudless days). This happens because of what is actually in the sea and has nothing to do with what is above it. The picture of Liguria, in Italy, pictured below, perfectly shows the different hues of the sea.

Oceans and lakes usually contain a lot of particles suspended in the water. These are a combination of dirt and dead plants and animals. Living animals, too, because of their size can change the way we perceive the color of a body of water. As the water fails to absorb a lot of blue light, it hits these elements in the water and the blue light is reflected right back upwards. Tropical water and, say, the waters of the Atlantic look different to each other because in the tropics the color is due to the absorption of the red light, leaving only the blue visible to us.

The colors of the waters off Guadalupe can be seen here in this amazing wave. The Atlantic on the other hand has a blue which is caused by the suspension of countless numbers of plant, animal and dirt particles within it.

Why do some bodies of water appear colors other than blue? Some look black or grey or even brown. Again, this is because of what is absorbed in the water. Muddy waters appear muddy because of sheer science. Mud reflects more red light than blue light and so when there is mud in water it looks brown. A lake full of peat will look black as peat absorbs virtually all the light that hits it. On a stormy day the sea will appear a grey color and, yes, that is partly to do with the color of the sky. It is also because the clouds filter out a great deal of the red light from the sun before it hits the water.

We see water in a variety of ways. It may be colored by particles, the presence of bacteria, or by reflecting the world above its surface. Ice and snow may reveal a vivid internal blue such as the Multnomah Falls in the Columbia Gorge in Oregon, above. Water itself has an intrinsic blue color that is a result of its molecular structure and its behavior. The blue bouncing back can be vividly seen here, as a pair of brace (foolhardy?) climbers venture up a waterfall in the Banff National Park in Canada.

Of course, the waters around Banff National Park are renowned for their turquoise color. This is due to the many particles of finely ground rock in the glacial melts. Lake Moraine, below is known for this icy blueness which almost hurts the eyes.

If you want to have a look for yourself at the natural and intrinsic color of water, you can do that fairly cheaply. Take a long pipe filled with purified water. So that the water doesn’t flood out when you look through it, cover each end with a transparent window. If you look down through the first of these windows at a piece of paper lit by natural sunlight you will see the pale blue color of water revealed.

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