Understand Water

It’s one of the strangest substances in the Universe, but we wouldn’t exist without it. Welcome to the wonderful world of water…

- Brian Clegg

When Earth is seen from the depths of space it appears as a blue dot. This is because just over 70 per cent of its surface is covered with water. Water is present on many of the planets too, and several moons of Jupiter and Saturn are thought to have significant water resources. But Earth is, without doubt, the one body in our Solar System where water has a defining presence. It’s thanks to water and its physical peculiarities that life has flourished in the first place. Water is so familiar to us that we often forget just what a remarkable substance it is.

What exactly is water?

Water is H 2 O, a simple molecule consisting of two atoms of hydrogen and one of oxygen. It is the only substance that exists as solid, liquid and gas in the temperature ranges found naturally on Earth. Water is transparent, but isn’t entirely colourless. Just as the sky is blue because molecules in the atmosphere scatter blue light more than other colours, so large quantities of water have a similar blue tinge, whether it’s the ocean or the dramatic blues of glacier ice (oceans and lakes also reflect a blue sky, making them appear even bluer). We are extremely lucky to have so much water on Earth because it has remarkable properties.

What’s so special about it?