Most people would answer that water is colourless or the colour of the sea depends on the sky, but we cannot trust in our eyes. Sometimes reality is not how we see it. The color of water depends on its volume and how the sunlight hits it. What colour is water?

When we fill a transparent glass, the water appears transparent. The same thing happens with a bucket. In a bathtub, a bluish hue begins to appear. Rivers and the sea also appear blue, whether the sky is grey or clear. This means that water is bluer when there is more volume. How is it possible?

The answer is simple. When light rays hit the water they contain all the colours of the visible spectrum. But some of the rays are reflected and they lose a small part of its spectrum: the red tones. Why? They are absorbed by the water. If we remove the red tone from white light, it will acquire a bluish hue. This is the colour that reaches our eyes.

The more volume of water we have, the more this effect is noticeable. That is why seawater is blue. This happens in small volumes of water as well as in large ones. The problem is that our eyes do not have enough capacity to appreciate it.

The colour of water can also change by other external agents. Algae will turn it green and sediments brown.