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What is the color of Water? I am not talking about large water bodies like Ocean or lake but a glass of water. If it has no color how can we see it?

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Perhaps, what about the color of water..? –  Waffle's Crazy Peanut Dec 15 '12 at 14:26
@CrazyBuddy: on that subject, I liked this book. –  Mike Dunlavey Dec 15 '12 at 14:41

2 Answers 2

up vote 2 down vote accepted

The water has an index of refraction, so it distorts what you see through it. That enables you to see it's edges, etc.

Pick up a pair of glasses - same thing. They have no color, yet they are visible.

Things don't need to be colored to be seen.

If you want something to be invisible, it only needs to have the same index of refraction as what it's embedded in.

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Was about to answer the same thing, so I am just sharing this cool refractive index matching video: youtube.com/watch?v=LVukK27rTbY –  Bernhard Dec 15 '12 at 14:26
Even I was thinking the same. But just wanted to confirm. Thanks for your answer. :) –  Inquisitive Dec 15 '12 at 14:31
@Bernhard: That's great, and there are many more like it. You shoulda got the votes. –  Mike Dunlavey Dec 15 '12 at 14:37
This answers the question well, but it is worth clarifying that pure water really is a blue substance. It's only slightly blue and it's hard to see the blue tint in a small thickness of water, like a glass of water. –  Steve B Dec 15 '12 at 15:31

A small amount of water is (approximately) transparent to visible radiation of all colors. The adjective "transparent" is usually not considered a color – although in some computer graphics system, one may include it among "generalized colors".

enter image description here

We can't really see water if it surrounds us. Imagine two parallel glass plates and water in between them. You can't really "see" whether there's water in between or nothing – the air – at least if you avoid experiments attempting to see how the object looks from different directions. Even when you look at the sculpture of Saddam Hussein above called "The Shark" above, you can't immediately say whether it's filled with water or not. But if you look more carefully, you will see that the vertical boundaries of the paintings behind the aquarium are significantly shifted which proves that the water is there in the tank. The location of the paintings is shifted because of the laws of refraction.

enter image description here

When we have finite volumes of water with the boundary, we may see the boundary because the light refracts off the boundary a bit differently than it does in the air. The light rays move essentially along straight lines in the air (or the vacuum) but when they hit the water-air boundary, they change the direction. Consequently, if you study what you see if you're looking in a particular direction, or a particular pixel of the picture above, you must continue the line differently and you end up at a different point, with a different intensity of the source, than where you would end up otherwise. This may display itself as a lighter or darker (or just different) color behind the water or even reflections of other objects. At any rate, one can see the difference between "water is there" and "water is not there" because in these two situations, the light rays propagate along different trajectories if they're supposed to reach our eyes from the same direction.

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