Water level when you fill a spa. There is a level on the filter face that says water line - Keep the spa water level at least 50mm above the skimmer at all times. Never allow the water level to drop below the bottom of the skimmer opening. If the water level is too low, the skimmer will allow air into the water lines of the pump, causing it to lose its prime (water -flow). Running the pump without water flow will damage the pump seal assembly and could result in further equipment damage, which will not be covered by the product warranty.