The bay-like decreases in water level changes with amplitudes 11 and 1 cm are registered in the wells UZ-5 and E-1, Kamchatka, within three weeks before the 5th December, 1997 Kronotskoye earthquake, Mw=7.8. Such decreases of water level were occurred synchronously with horizontal displacements of the GPS - stations located on distances up to the first hundreds km from the source of earthquake. The generation mechanism of the Kronotskoye earthquake precursor in the water level changes is discussed on the base of elastic statically confined response of water level under the seismotectonic deformation of water-bearing rock. The water level decreases in both wells are explained by the undistorted response of pore pressure to a quasi-elastic volume deformation of the water-bearing rock as a result of pre-seismic movements in the source of the Kronotskoye earthquake. The estimated values of a pre-seismic expansion of the water-bearing rocks are Dt = (0.6-0.8) 10-7 in the area of wells.