Why is water blue?
The blue color of water is clearly seen when we look deeper into the waters. The blue color of the water is also observed in Caribbean Sea, Mediterranean Sea and in Colorado Mountain Lake. The pure water and ice have pale blue color in sand beaches or in ice holes in glaciers. The blueness is not due to any impurities or scattering. Since the absorption of light will be at the red end of the spectrum, the reflected light will be blue which is considered as complimentary color of orange. Snow and ice which form a thick layer appear blue due to scattering of light especially in deep holes in the ice.
The water appears blue due to vibrational transitions of the water molecules. The blue water is the one and only example for this phenomenon. In many of the cases, the color of an object will be created due to absorption, emission and selected reflection of light. Other non-resonant interactions of photons with electrons include scattering, interference, diffraction and refraction. All these mechanisms depend on the photon interaction with electron while blueness of water is not due to these mechanisms.
The blue color of water is due to its absorption in red part of the spectrum. The light that is absorbed consists of photons which enhance the motion of nuclear particles and transition of the particles to their higher states. Water absorbs light wavelength that is above 700nm. The absorption spectrum of water shows that light of shorter wavelength penetrates it and imparts blue color to it. Sea water at some places might appear green due to the presence of algae or due to scattering of light by any suspended particles. The sea water also appears blue due to reflected blue color of the sky or scattering of light from the deep waters.
The light of lower energy was not found to be able to penetrate deeper and hence only the higher energy blue light wavelength can pass deeper through the waters. So, as we go deeper and deeper in the sea the water appears intense blue while it appears light blue on the surface.