• Question: What colour is water?

    Asked by anon-181367 on 6 Jun 2018.
    • Photo: Alex Haragan

      Alex Haragan answered on 6 Jun 2018:

      Pure water is virtually colourless, as well as free from smell and is of course transparent.
      However – pure water is pretty rare outside of the lab.

      Most of the time there are things dissolved into the water that give it colour, or in the case of water outside it can be discoloured by things living in it (algae often give the impression of a green hue) and the reflection of the sky gives the oceans that blue colour.
      Even bottled water and tap water will have various chemicals in them that will give it a taste and small amount of colour.

      Apparently water is not totally colourless though – and if water becomes deep enough, even pure water would have a faint turquoise colour. This is due to the properties of water that make it reflect and absorb certain parts of the visible spectrum – but you should ask a physicist for a more in depth explanation if you need one!

    • Photo: Lauren Burns

      Lauren Burns answered on 8 Jun 2018:

      Alex is right, water can change colour dependant on what is in it. However, the reason pure water is ever so slightly turquoise, is because all light is made up of different colours. When light travels through a ‘medium’ (like water), different colours scatter and are absorbed by the medium in different ways. Blue is absorbed less than red, yellow or green. As it is the blue light that escapes (i.e. not absorbed), it is the colour that we see. If you really want to annoy a physicist, the question you should ask them is why the sky and sea aren’t purple – as purple should be absorbed less than blue!!!

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