Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)

Why is water clear?

Water is clear because nothing in it reflects light.

You can see things because light from them gets into your eyes. If something has nothing in it to bend or bounce light, you don’t see it. This is why air and glass are both clear.

There are times when you can see these things. If the air has dust in it, you see the dust. Or if the air in one place is hotter or colder than in another place, you can see the effect of the difference because it bends the light, and things on the other side look distorted or appear to move.

If glass is perfectly clean, you might not know it is there and walk into it. But if the glass is not smooth and flat, you can see how it distorts things you see through it, and you can tell where it is. If the water or glass has a dye in it that absorbs some color of light, then you see all the colors but that one, and you know the glass is there. If the glass absorbs yellow light, it will look blue.

Water and most glasses actually do absorb red and yellow light more than they do blue, so if there is enough water or glass, it looks blue.