[Physics] Why does water have no color

Question

When a substance absorbs and reflects light, it shows the color of that absorbed and reflected light. But water is colorless. Does it absorb and reflect light. What is the reason for this?

Answer 1

Liquid water has very little absorption in the visible light - this is why it looks colorless.

There is a very extensive article on the absorption of electromagnetic radiation by water on Wikipedia.

A few highlights:

• there is a difference whether you are talking about solid (ice), liquid ("water") or gas (vapor). This has to do with the fact that much of the absorption is a result of molecular vibrations - and not all vibrations are possible in all states
• Liquid water has very low absorption in the visible spectrum. Here is a plot of the absorption (note - this is for PURE water; contamination will greatly affect the transparency. For example, fine particles in water will preferentially scatter blue light):

Attribution: Darekk2 on Wikipedia, based on

• Pope R. M., Fry E. S. Absorption spectrum (380-700 nm) of pure water. II. Integrating cavity measurements. Appl. Opt. 36, 8710-8723 (1997), eprint.
• Kou L., Labrie D., Chýlek P. Refractive indices of water and ice the 0.65- to 2.5-µm spectral range. Appl. Opt. 32, 3531-3540 (1993), eprint.

From the Wikipedia article:

The absorption was attributed to a sequence of overtone and combination bands whose intensity decreases at each step, giving rise to an absolute minimum at 418 nm, at which wavelength the attenuation coefficient is about 0.0044 m$^{−1}$, which is an attenuation length of about 227 meters. These values correspond to pure absorption without scattering effects.