Why is the colour of water blue?

Answer 1

Water is blue because it weakly absorbs the red end of the light spectrum well, just like other blue items. The degree it absorbs the red is very difficult to perceive with small amounts of water, which is why a glass of water is colorless.

It is a common misconception that water is transparent or colorless (which is ironically perpetuated by claiming that the opposite is a misconception), but water's color can and has been shown experimentally. The reflection of the sky, a common explanation, would only alter the water color if it was very still, which it often is not. Water is still blue on cloudy days.