Why is water different colors? (Rain, water in a glass, oceans/lakes)


I understand why the ocean and lakes are blue, water absorbs red light out of the spectrum so it appease “blue” to over simplify. But is water in a glass, or drops of rain, look clear? What’s the difference?

In: 1

Water isn’t different colours. Water is always clear, itstuff in and around the water that makes it look like different colours.

Water is very slightly blue, with *heavy* emphasis on the “very slightly” part.

You need an enormous amount of water to see the effect, which is only observable after the sun’s light has passed through water for a long distance and slowly filtered out the reds.

You won’t notice that 0.000000001% of the red light has been filtered out from a raindrop, just like you probably don’t notice the window glass in your home is slightly green.

Water is always the same color, more or less. The apparent difference comes from a bunch of combined factors:

* Volume. Water is not actually perfectly clear. It’s got a very slight tint to it, so when you see a whole lot of water in one place, it’s like looking through a series of many color filters stacked on top of one another.
* Reflection. Water is somewhat reflective and the sky often appears blue-ish. Water, on a day with a blue sky, can look bluer than normal.
* Contaminants. Lots of stuff gets mixed and dissolved into water, any of which can change its color or simply make it more opaque. Salt or sand or silt or industrial pollution or…etc… Of course, those won’t necessarily make it appear *blue*, but it’ll give water *a* color.

Water is mostly transparent with a hint of blue. It is transparent because it absorbs/scatters very little light over most of the visible spectrum. It is a bit more transparent to blue than the other colors.

Even though water is transparent, it is not perfectly so. Some of the light is absorbed/scattered and the longer the light’s path through the water the greater the attenuation. Since blue light is less absorbed/scattered by water it is less attenuated and becomes the dominant color. It should be noted that not only does water become bluer the longer the lights path through it, but the overall brightness of the light also decreases.

Imagine a clear piece of cellophane with just a hint of blue to it. You can see through the sheet without problem. Now start stacking the sheets while looking at a white light. The more sheets you stack the more blue AND darker the color. Now imagine making that cellophane with just a bit less of a blue tint so that a single sheet appears clear. You can stack more sheets before it will appear blue, but it will still ultimately look blue with enough sheets.

The water in a drop, in the glass, or in your bathtub is like a couple sheets and will appear clear. To simulate deeper bodies of water you just stack more and more cellophane sheets.

It should be noted that actual bodies of water have other materials present that will change the color of the water–for example organic materials generally absorbs the smaller wavelengths more–blues and violets. This leaves more of the light in the middle of the spectrum since both the blues and reds are scattered/absorbed. So a pristine water source with little suspended particles will appear blue, but one with a large suspension of organic material may appear more greenish.