By analysing several years of discharge and electrical conductivity data from an artesian well in Kajaran, Armenia, we found a significant sensitivity of this well to distant large earthquakes. In general, the discharge increases co-seismically and the conductivity decreases post-seismically with a time delay of about 1 hr. The post-seismic trends of the conductivity reach a minimum after about 3 weeks and then need several months to recover to the pre-seismic level. For instance, the Izmit earthquake in Turkey on 1999 August 17, at a distance of 1400 km, led to an increase of 25 per cent in discharge and a decrease of up to 6 per cent in conductivity. The discharge also shows tidal fluctuations of amplitude roughly 5 per cent (peak-to-peak) of the mean well production, whereas the tidal signal in the conductivity data is less significant and unstable. The maximum co-seismic static strain estimated for 11 earthquakes that induced an anomaly during the monitoring period is below 10−9, or at least one order smaller than the tidal strain. Therefore, the well-water anomalies related to the distant earthquakes are believed to be induced by seismic ground shaking rather than co-seismic deformation. We suggest mixing of groundwater as an explanation for the observations and present a model which considers specific conditions for this particular groundwater system: a confined aquifer with a high contrast in the hydrogeochemical composition between two different groundwaters and a macrofracture as the mixing zone which is hydraulically connected to the artesian well. The earthquake-related anomalies are believed to result from a local head increase near the artesian well, induced by the passage of seismic waves. Possible mechanisms are discussed, and the time histories of the anomalies are modelled. [ABSTRACT FROM AUTHOR]