What colour is wa­ter?

Focus-Science and Technology - - Q & A - ASH­LEY MARTIN, RM

We usu­ally think of wa­ter as a colour­less liq­uid, but it’s not true. When white light is shone through a long col­umn of the stuff, the liq­uid is faintly blueish. That’s be­cause the wa­ter mops up the longer, red­der wave­lengths of light, leav­ing the bluer wave­lengths un­scathed. As with so many of its prop­er­ties, how­ever, wa­ter does this in a bizarre way, with the light en­ergy be­ing ab­sorbed by its V-shaped H2O mol­e­cules, which start to vi­brate as a re­sult.

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