Experimental studies on the measurement of the conductivity of distilled water in a slowly changing its temperature were performed. We detected periodic variations in the electrical conductivity of the water, in observed rate of change of the temperature $dT/dt<0.1$ K/h. Period is more than a day, variations in the amplitude range from + 2.7% to - 2.3%. Possible reasons for the observed phenomena is discussed.
51.20.+d Viscosity, diffusion, and thermal conductivity
67.80.Mg Defects, impurities, and diffusion
$^1$Moscow State Aviation University (MAI), Moscow 125993, Russia.