Water as a multifunctional resource is necessary to sustain life on Earth because of the many beneficial effects without which life would not be possible. With each use of water, we change its natural composition and impair its quality with polluting agents of different structure and thus create wastewater. Such polluted water must not be released directly into nature before adequate treatment due to the devastating impact on the environment, but also the harmful impact on human health. Wastewater treatment is performed using biological, chemical and physical procedures, and includes the removal of unwanted chemical compounds, organic and inorganic materials and biological contaminants. The general objective of wastewater treatment is to increase the quality of the environment by discharging as little polluted water as possible, to improve the quality of life and to protect human health. Monitoring the efficiency of the treatment process and quality control of treated water is carried out in laboratories in accordance with the Regulations on limit values for wastewater emissions (OG 80/13, OG 43/14, OG 27/15, OG 03/16). Specific parameters are analysed, the values of which provide information on water quality, and the permissible values are prescribed by the aforementioned Regulations. If the obtained values of these parameters are in accordance with the values in the Regulations, the water is discharged into the watercourse. If the determined values are higher than the allowed ones prescribed by the Regulations, it is necessary to conduct additional tests and analyses in order to determine the origin of the excess of a certain component in wastewater and to reduce their concentration by modifications of the treatment process. This paper describes the methods used to analyse and monitor the quality of treated wastewater.