The ГК-1 self-discharging well is located in the southeastern part of the Kamchatka Peninsula. The well is part of a network of continuous observations of the groundwater regime, conducted in order to identify and study the hydrogeochemical precursors of strong Kamchatka earthquakes. The article discusses data on changes in the flow rate and chemical composition of well water for the period from 1970 to 2022. The subject of the analysis is the hydrogeochemical effects appearing under the conditions of non-stationary regime arising due to drainage of the pressure reservoir by the well and as a result of changes in bottom-hole pressure. The mechanisms of formation of long-term (decades) and relatively short-term (tens of days) changes in the chemical composition of water at the mouth of the ГК-1 self-discharging well are discussed within the framework of the concepts of water-bearing rocks as a heterogeneous block medium with double porosity.