Drinking-water is one of the most frequently checked foods, that is always available. Nothing can replace it’s refreshing effect. In the operation area of Nyírségvíz, the resources of drinking-water are subsurface ground waters, that are free of external contaminations, but cannot be distributed into the water network in their original form. The drinking-water is being exploited from deep-drill wells, with the help of submersible pumps. As the iron and manganese content of the raw water is over the threshold values, it must be cleaned before distribution. The water-cleaning technology includes mostly the removal of iron and manganese, respectively disinfection. Over-content of iron and manganese are not health-hazard, but they cause some difficulties in the use of water (yellow coloured deposition in the pipelines). After Hungary became a member of the European Union, the threshold values of arsenic and ammonium became stricter; thus, in some settlements we have to find a solution to agree these stricter water-quality prescriptions up to 25. December 2009. In case the arsenic and ammonium content exceeds the threshold value only lightly, their content can be reduced in one step, with the help of the traditional iron and manganese removal technology; but, in some cases, a new step in the cleaning cannot be avoided. The arsenic and ammonium content of the wells is exclusively geological origin, is not an external contamination. Even the earlier threshold values according to the Hungarian water quality standards did not mean any risk for the human health. Drinking water gets from the place of exploiting to the consumers through a very long way. This is especially true in Nyíregyháza, where we consume the water produced in Kótaj, Paszab and Nyírtelek, that shall be forwarded to the city through pipelines. To hinder any water-connected epidemic, water must be disinfected. Disinfection is done mainly with chlorine gas. Chlorine addition is a necessary part of the technology, that cannot be avoided, otherwise, without disinfection, between the temperature and pressure conditions of the pipeline network, some bacteria could be multiplied, that would cause illnesses. Parallelly, we do our best efforts to keep the detectable active chlorine content of network water at such a minimum level, that is enough for the maintenance of the immaculate microbiological status.