A grid is made up of thousands of rows and columns of LEDS. When they come into contact with water, they suddenly light up. The water conducts electricity, forming the missing link in a small electrical circuit. This means that you can paint and draw on the surface of the lights with water. You can use anything to write with – a plant humidifier, a water pistol, a garden hose, a damp paintbrush or your own wet fingers – anything wet will leave a trail of light.