A liquid level controller for a waterpan-type spray booth. The controller comprises a normally-open first air pressure sensor and switch for detecting a minimum level of negative static pressure through the restricted opening indicative of ventilation fan operation and for closing the first air pressure sensor and switch to thereby permit a voltage output. A normally-closed second air pressure sensor and switch is provided for sensing a predetermined negative static pressure level indicative of a minimum adequate air flow through the restricted opening for opening the second air pressure sensor and switch to interrupt a current flow through the second sensor and switch. The normally-closed second air pressure sensor is normally closed by the voltage output from the normally-open first air pressure sensor and switch. The first and the second air pressure sensor and switch are operatively connected to a water supply valve. A decrease in negative static pressure resulting from a drop in water level in the water pan and a consequent increase in the size of the restricted opening defined by the water level and washing enclosure returns the normally-closed second air pressure sensor and switch to its normally-closed state. This permits opening of the water supply valve to raise the water level in the water pan. This decreases the size of the restricted opening and increases the negative static pressure to re-open the normally-closed second air pressure sensing and switching means and close the water supply valve.