Raw water, i.e. the water we use from water-based drinking facilities in order to supply the population with drinking water could be of various chemical and microbiological composition as it necessarily contains dissolved and suspended substances from the environment that water runs through, either the soil, or the atmosphere. Water quality, in microbiological and physico-chemical terms, is defined by selecting and analyzing water samples, and the valid drinking water is defined according to the Regulations on compliance parameters and methods of analysis of water for human consumption (NN 125/2013) (Pravilniku o parametrima sukladnosti i metodama analize vode za ljudsku potrošnju). After analyzing the results, it is determined whether and to what extent the conditioning should be performed. Methods for drinking water preparation include a number of primary and secondary processes that are combined within the technological process. In water conditioning practice we most commonly use the following processes: precipitation, coagulation and flocculation, filtration, disinfection, and other special methods and processes (water softening, defluorisation - fluorination, taste and odor removal, micro pollutant removal). For various processes and operations of drinking water conditioning, it is necessary to design highly complex objects and devices, which must contain optimal hydraulic and technological characteristics. This paper presents the methods of drinking water conditioning with an emphasis on drinking water treatment of Slavonski Brod. ”Jelas” drainage plant drains and treats groundwater and it prepares it for human consumption. The drainage plant has 8 wells, each of which has a water discharge capacity of 50 l/s. Determining the values of individual parameters after certain stages of water treatment we researched the process efficiency and established compliance with the Regulations on compliance parameters and methods of analysis of water for human consumption (NN 125/2013) with the emphasis on the critical parameters of the process: ammonia, manganese and iron. The conditioning of raw groundwater from the “Jelas” pond is performed by filtration on dual-medium filters, filtration on activated charcoal filter with previous water ozonization.