This paper presents evidence on the quality of ground and surface waters in the Krestovaya Valley used for community water supply. Ground water of HCO3 Mg–Ca (Ca–Mg) composition with TDS ranging between 71,0 and 514,5 mg/L is commonly available in Listvyanka settlement. It was analyzed how the water components comply with the requirements of the threshold level value for potable water, and thereby established that the content of all components in the local ground water sources does not exceed critical concentrations. However, some water wells have been found polluted. The main pollutants are nitrates, ammonium and silicon, originated from discharged residential wastewater of numerous hotels situated along the Krestovka River banks. The threshold level values of nitrates and ammonium in the groundwater are found to be 1,1–5,9 and 6,3 times higher, respectively. Given that silicon content of both the riverine and ground water is almost equal, it may be taken as the natural background content, despite their pollution level is in excess of permissible limits. The problem of potable water desilication through water treatment processes should be solved on the basis of socio-hygienic monitoring and eco-epidemiological studies. To monitor ground and surface waters quantity, a depth-to-water map of the valley has been compiled which shows the stream underflow course from watersheds toward the Krestovka River and Lake Baikal. The stream underflow is formed at the confluence of groundwater of crystalline rocks of bed-rock massifs and groundwater of Quarternary alluvial deposits.Keywords: ground water, water chemical composition, nitrate, nitrite, phosphate, threshold level value.