Water molecules are attracted to each other, this is known as cohesion. This attraction arises from electrostatic interactions known as hydrogen bonds. Hydrogen bonds, between water molecules, are intermolecular forces that form between the partially negative oxygen atom from one molecule to a partially positive hydrogen atom from another water molecule. This causes the water molecules to ‘stick’ to each other. Have you ever noticed droplets of water on a leaf? This is caused by the cohesion of water.

Cartoon depiction of adhesion and cohesion. Two cartoon water molecules, oxygen is represented as a red sphere with an unhappy face with two white hydrogen atoms attached at the top. The oxygen atom from the first water molecule is holding hands in the middle with the hydrogen atom from the second, this is highlighted in yellow with the label cohesion. To the sides the two oxygen atoms are holding onto the sides of two brown lines representing another surface. This is highlighted in blue and labeled adhesion.

Sometimes, water has an even stronger attraction to other molecules than itself. This is known as adhesion, and occurs with other polar and charged molecules. The principle is the same for cohesion, where water forms hydrogen bonds, but rather than forming hydrogen bonds with water molecules, it forms them with molecules of another kind.