This paper analyzes the parasitological state of natural water bodies — rivers, lakes, springs, wells, as sources of drinking water supply, according to the content of round and flat helminthes. It is shown that climate aridization, which has been taking place in recent decades, causes, first of all, a decrease in the hygienic safety of surface water sources and an increase in the number of some helminth eggs in them, in particular, cestodes, which is associated with an increase in the average annual temperature under conditions of climate aridization. The water of surface water sources has an unfavorable parasitological composition in the presence of helminth eggs in the invasive and non-invasive stages of the life cycle. Reservoirs of the middle and southern latitudes are untidy from the point of view of the parasitological background in terms of the content of helminths. Contamination of water supply sources by eggs and larvae of parasitic worms in arid regions is confirmed by the morbidity of the local population. In the article, we noted various topical methods of preventing specific parasitic diseases — medical examinations of the population, parasitological studies of drinking water, parasitological control of raw materials and fish products, hygienic education and medical examination of the population for the purpose of early active detection of the infected. The presented up-to-date information on the results of sanitary and parasitological studies of environmental objects in different regions of Russia showed that the greatest contamination of round and flat helminths with eggs is characteristic of the southern regions. The example of the Saratov region shows the change of the fauna of endoparasites from humid to subarid and arid regions — nematodes are represented in the Right Bank of the region, and cestodes (Echinococcus) in the Left Bank. Cestodes are most characteristic of an arid climate.
