Why does water transmit light?
Actually, a lot of pure liquids transmit light. To explain why, it’s easiest to start by explaining why water doesn’t do other things. It doesn’t absorb light because when a photon is absorbed by an electron in a water molecule, the water molecule usually re-emits the photon without any loss of energy. If water absorbed light (as it does with some other electromagnetic wavelengths) the energy of the photon would not be released by the electron but instead would be converted to heat. It doesn’t scatter light because water is a homogenous fluid. It contains no objects or structures that are larger than a wavelength of light. Milk is basically oil droplets suspended in water, two transparent liquids, but it scatters light because the oil droplets are larger than a wavelength of light. So photons of visible light pass through water, slightly delayed because of interactions with electrons on the way through. For a much better explanation of how light interacts with transparent materials, I
