This work describes the results of the research of underground water from artesian wells and wells in Causani region of the Republic of Moldova. In the studied region in spring, 2021, 13 samples of water from artesian wells and 9 samples from wells were taken. All the sampled wells are important sources of drinking water. All samples were analyzed for various chemical parameters, such as hydrogen sulfide and dissolved sulfides, ammonia and ammonium ions, nitrites, total harness, sodium ions, iron ions, fluorides, sulfates, chlorides, oxidability, total dissolved solids. All the parameters were determined according to standard techniques. It was shown that water from different artesian wells and wells of Causani region of the Republic of Moldova are considerably different. Water from artesian wells are characterized by elevated content of ammonia and ammonium ions, hydrogen sulfide and dissolved sulfides, sodium ions and fluorides. At the same time, the content of hardness salts is below the minimum allowable value for all the samples. In water samples from wells, the most commonly exceeded parameters are nitrates, hardness salts, sodium ions, sulfates and total dissolved solids. For quality assessment of the analyzed water sample we used water quality index (WQI). WQI allows to transform extensive water quality data to a single value, reflecting water quality level, thus erasing the differences between the parameters used in the assessment independently. WQI was calculated by 11 chemical indices, maximal allowable concentration of are set in the national legislation (Law № 182 19.12.2019). WQI was calculated in four steps. The first step was assigning a weight (wi) to each parameter depending on its effect on human health. The worse the effect on human health, the higher the weight assigned. The allotted weight ranges between 1 to 5. The second step was the calculation the relative weight (Wi) using the formula: Wi= Σ , where the relative weight is represented by Wi, wi indicates the individual parameter weight, n represents number of groundwater parameters. The third step was to estimate the quality rating scale (qi) of each parameter using Equation: qi= *100, where Ci is the concentration of each parameter in mg/L, Si is the standard permissible value for the i parameter in mg/L. The fourth step was to calculate the WQI using Equation: WQI=Σ * qi. Based on the WQI value the water is classified into five categories: excellent (WQI<25), good (25 <WQI<50), poor (50 <WQI<100), very poor (100 <WQI<150) and unsuitable for drinking (WQI> 150). Quality assessment of water from Causani region of the Republic of Moldova on the basis of WQI showed that 15,4% of water samples from artesian wells belong to the category poor, 53,8% - very poor и 30,8% - unsuitable for drinking. Quality assessment of water from wells on the basis of WQI showed that 66,7 % of samples belong to the category very poor, 11% - poor and 22% belong to the category good. Using WQI method, it was shown that none of the analyzed samples from the artesian wells was in the categories excellent or good. Only 2 water samples from wells were in the category good. The present research revealed an important challenge of providing the population of Causani region with the access to a good quality drinking water and showed the importance of up-to-dated technologies of water purification for facing this challenge.