Why does pouring water have a slightly different color when viewed from above?

Question

I have noticed when I view a hose pouring water the color of water slightly changes when looking from above compared to when looking from the front.

Also, the same thing applies when you pour water from your mouth. If you look at it from above there's a color I can't describe very good (but I think there's a yellowish in it). But when you look at yourself in a mirror pouring water from your mouth, the water is colorless.

To see the phenomenon better do it immediately after you've finished brushing your teeth. Just put a little water in your mouth and pour it down (looking from above).

Why do I perceive this color change?

Answer 1

This might be because the water would faintly reflect the colour of your skin or something directly above you. When you see it from the top, what you see is the reflection of a pale object (probably your face).

When you're looking at it from the side, only the water would reflect. When seen from the top, the water as well as the surface beneath (of the vessel you're pouring it into) would be reflecting light (hence more visible colour).

Answer 2

I think it is possible that your surroundings play a role in that. Like maybe you have yellow lights in your washroom or something like that.

Answer 3

I agree with Maddy.

However, there's also another possibility.

Like a prism, water can also disperse certain wavelengths of color into other colors. Its refractive index, which is a measure of how well is refracts or change the direction of light, refracts different wavelengths at different angles (for more, refer to Light Dispersion in Water). This causes you to perceive different colors reflected from the water. In your case, the color you perceive could just be the dispersion of a light source in your room.

You might wonder: Wouldn't I see a rainbow then? The simple answer to that is that a water by itself can be seen as a round-is shape. This means that if you look from inside the water, you might see that, when you pour it, its cross section is irregularly parallel (imagine light traveling from one "side" of the water to the other "side").

This is why we use a prism for "ideal" dispersion. Its tilted, non-parallel shape allows light to disperse without being regrouped.

Water's "shape" doesn't allow entirely ideal dispersion. This means that only certain wavelengths can disperse in different conditions, which is an explanation as to why you only see one wavelength or color.

However, if you pour water into a relatively circular glass and and shine concentrated white light into it, you can see a rainbow!

If you want to calculate the refractive index and angle of refraction of different wavelengths, although I would advise against it as it would be rather complex and would not deepen your understanding of this phenomenon, you can use Snell's Law :)