This flow indicator is used as an optical flow control in the water circuit. The flow of water sets the wheel in motion, and the rotating paddle wheel indicates the flow of the liquid. Malfunctions such as kinked hoses can thus be visually monitored. The filter has also proven to be non-obstructive even at high flow rates. It captures even the smallest particles in the water circuit, which is particularly useful when a nozzle cooler is present in the circuit, as clogs can be virtually eliminated.