A filter appliance including a dilution device, wherein the diluted portion remains largely constant when the entire volume flow is modified. Said filter device is characterized in that the flow characteristic--defined by the pressure loss function .DELTA.p.sub.B({dot over (V)}.sub.B)--of the constituents of the dilution line B is adapted to the flow characteristic defined by the pressure loss function .DELTA.p.sub.A({dot over (V)}.sub.A)--of the constituents of the filter line A, in such a way that the dilution condition holds good for at least one diluted portion X where X={dot over (V)}.sub.B/{dot over (V)}.sub.A+{dot over (V)}.sub.B for volume flows between be {dot over (V)}.sub.1=10 liters per hour and {dot over (V)}.sub.2=120 liters per hour, first volume flow range, for at least one second volume flow range of at least 5 liters per hour inside the first volume flow range, .DELTA.p.sub.A({dot over (V)}.sub.A) designating the pressure drop over the dilution line B according to the respective volume flows {dot over (V)}.sub.A, {dot over (V)}.sub.B in liters/min of the water in lines A and B.