eli5: Why is water clear in small quantities but blue when in large quantities?

Question

eli5: Why is water clear in small quantities but blue when in large quantities?

In: 3

Answer 1

Because water IS blue AND relatively transparent.

Water is blue because it absorbs colors other than blue much more. Thin layers of water doesn’t absorb much light so you don’t notice the color. As the layer gets thicker, more and more light gets absorbed and the color gets darker. If you get deep enough in the ocean, the water no longer looks blue–it looks black because almost all of the light (including blue) are absorbed.

Imagine a gray scale gradient from white to black. Replace the gray with the color blue. The bright side will still be white and the dark side will still be black, but in between you’ll see a lot a shades of blue.