Abstract: Continuously operating inside flow filter for placement within a pressure tank, comprising one or several filter cartridges filled with a filtering mass and an alkalizing mass placed around a sludge cylinder fitted upon a bottom grating, and the pipe system associated with the equipment, with valve control. Both the water filtering and the flushing have been arranged to take place by operating one single three-way valve known in itself, in such manner that during filtration this valve and the drain valve in the bottom of the tank is closed and the water flows from the water mains through the three-way valve and a check valve and through a pipe into the lower part of the tank in among the mass, whereby the iron will be precipitated.