Question

WHY IS WATER TRANSPARENT AND COLOURLESS?

Answer 1

Hence, small quantities of water appear to be colourless. But water's tint becomes a deeper blue as the thickness of the observed sample of water increases. The blue hue of water is an intrinsic property and is caused by selective absorption and scattering of white light. Water is optically transparent.

Answer 2

Here is your answer
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Pure water is transparent because although it absorbs wide ranges of invisible wavelength, it does not observe or interact with visible light and allows it to pass through unaltered.

One reason for water transparent could be evolutionary. The eye of vertebrates involved in the sea, and grew sensitive to those wavelengths of light that pass through sea water.

Since the wavelengths we can see are those that passed through water, we perceive water has being transparent. Pure water does not significantly observe any colour from the visible range, so it appears colourless.

However, when light penetrates several metres of water, some wavelengths in the red end of the visible spectrum are observed. As a result, the deep waters of many lakes and seas appear blue in colour.
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