Why is a small amount of dilute acid added to water before electrolysis?

Adding a small amount of dilute acid to water before electrolysis is primarily done to increase electrical conductivity. Pure water has a very low concentration of ions, which makes it a poor conductor of electricity. By introducing a dilute acid, one adds ions to the solution. These ions (hydrogen and anions from the acid) enhance the solution's ability to conduct electrical current, thus facilitating the electrolysis process.

This increased conductivity allows for more efficient electrolysis, leading to a more effective separation of the water into its constituent elements, hydrogen and oxygen, at the electrodes. The presence of these ions is what enables the flow of electricity through the solution, making the process of electrolyzing water feasible.