Heterotrophic plate count (HPC) is the common name for a bacterial group present in the water which, under defined conditions, can grow on nutritive agar by using simple cultivation methods. In order to grow, they need a source of organic carbon. Throughout history, the role of this parameter has been changing. Today, it is predominantly used as an indicator of water disinfection efficiency and common hygienic conditions within a water distribution network. There is no universal method for determining the heterotrophic plate count. The method that provides the best results must be applied. This study analyses the presence of HPC/22 and HPC/37 in different types of water (untreated, processed, and pool water) in Primorje-Gorski Kotar County between 1998 and 2015. Untreated water showed the highest growth in HPC/22 colonies, while processed water showed the highest growth in HPC/37 colonies. Freshwater swimming pools showed higher growth of HPC/37 when compared to the pools filled with seawater. Furthermore, additional parallel tests of colony populations were carried out using different methods (media type, temperature, and incubation time) on water samples used for dialysis and swimming pools. In seawater pools, the application of Marine agar (instead YEA) yields significantly higher amounts of HPC/37. In water used for dialysis, the application of TGYA/22°C/7d yielded the largest number of colonies, indicating the underestimation of the number of colonies obtained by application of HR EN ISO 6222:2000. Because this water is used for a group of immunocompromised people, these results are of special importance. The results of this study indicate that the choice of cultivation method has a significant effect on the results of tests (both quantitative and qualitative), and that the only comparable results are those obtained using the same method.