• Question: what colour is water, and why do you see water different colours, like in the ocean it looks blue or green, but in the pool it looks pale blue, but in the tap and a glass of water, it looks clear

    Asked by to Kieren, Rowena, Roy on 19 Mar 2014. This question was also asked by .
    • Photo: Rowena Fletcher-Wood

      Rowena Fletcher-Wood answered on 19 Mar 2014:

      Water is blue. The colours we see in water are often due to reflections from outside objects, or objects seen through it because it is very translucent. Colour also comes from minerals in the water, like dissolved metal ions and clays/sands. This is why some seas like the Red sea get these names.

    • Photo: Roy Adkin

      Roy Adkin answered on 19 Mar 2014:

      Wow…excellent question Scarlett!
      Water…pure, pure water…is ever so slightly blue due to a tiny bit of fluorescence due to the electrons on the oxygen atom (remember water’s formula is H2O) but you’d barely notice it without a fluorimeter. Any colour you see in large bodies of water is due to impurities of particles in the water. The sea when it is green/yellowish is that colour because of organic matter dissolved or suspended in it…in the clearer oceans it may be because the water is more saline (it has more salts like sodium chloride or magnesium sulfate…to name just two!) and so makes it appear clearer and bluer. The water can also attenuate light and scatter it which causes the longer wavelength light to me absorbed leaving the shorter blue wavelengths. There is a place near where I grew up called Blue Pool in Poole in Dorset which is a an old Kaolin mine (a type of white clay used to make fine bone china) that has been filled with water. It is a nature reserve now and the visitors love it because the pool changes colour depending upon the sunlight…the brightness and the angle of the sun’s rays…it changes every colour of blue you can think of. The reason is tiny particles of clay suspended in the water reflecting and scattering the light.

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