In order to prevent the rolling brush from being too dry and unable to clean the floor well, a small amount of water will be sprayed to moisten the rolling brush when the WetVac is first powered on. It is also for the convenience of cleaning and the water dispensed is approximately 10ml. You can then choose whether to continue spraying water by pressing the water spray button. Please refer to the following article for more details: How to Use the Water Spray Function on the WetWac W31