Water enters shallow wells from shallow resources of groundwater, therefore the groundwater is especially susceptible to chemical and microbiological pollution. The aim of this study is to determine the effect of intensity of shallow well usage on the nitrate concentration in water. It has been found that concentrations of nitrate ions in the water of shallow wells depends on the quality of water in the basin feeding the well, processes in the water and well depth. Concentration of nitrate ions in newly filled water is higher than that in well water, but due to chemical and biochemical reactions it decreases rather fast and in most cases becomes lower. The rate at which the drained wells refill is different. Re-establishment of the same amount of water ranges between two and five days. In the beginning because of big difference in levels, the rate is higher, and then it slows down and asymptotically approaches the main level. An average rate of filling-up makes 3% of well volume per day, ranging from 7% the first day to 1% the fifth day. The nitrate concentration decreases approximately to eight days at a rate of 8 mg l^-1/day, and after the eighth day it increases at a rate of 12 mg l^-1. Changes of concentration of nitrates in the top layer of water could be summarized as the reaction of the first order. Mathematical patterns of well refilling and changes in nitrates determine the limits of the nitrate concentration changes in water, though they are not precisely adapted to a separate well.