As a primary cooling and smoothing agent, hookah bases contain water. Moisture particles are attracted to the smoke as it passes through the water.
By cooling the vapour, any coal or ash particles or ash will remain at the bottom of your hookah, rather than being drawn directly into it. In addition, your hookah will become heavier as a result.
Water is necessary for hookah smoking because it cools and diffuses your smoke, allowing you to enjoy it more comfortably.