This paper deals with the construction of the demanganisation device for the raw water from the wells B-4 and B-5 which are located in the well field Petruševec in Zagreb. The wells are being managed by the company "Water Supply and Sewage" Ltd., one of the sister companies of Zagreb Holding company. The metal manganese presence detected in the raw water of the two wells prompted the management to undertake measures to permanently and adequately resolve the problem. It was necessary to find and contract the best expertise for construction of a functional and efficient device for adressing metal issues as well as large deposits found in the water system supply pipes and water turbidity. After international tender was launched the jointly submitted bids by "Koncar-Engineering for the Industry" p.l.c. from Zagreb and "OTV" Inc. from Saint-Maurice Cedex France were chosen. The French company "OTV" provided the technical project documentation which was based on the filtering of the raw water from the well through positionning of the - manganese - dioxide filler in the direction from top to bottom. The proposed procedure is inexpensive, simple and without chemicals. The cost of the device is electricity consumed and replacement of the filter filling after 15 years of exploitation.