The protected technical monument “Janov Water Reservoir” is located in the Hamerské Valley near Litvínov. The reservoir was finished in 1914 and a hundred years after the completion we participated in its repairs. It was necessary to remove leaking that increased the risk of accident. An improvement to be reached by sealing the rock massif by the grout curtain constructed out of the new grouting tunnel. The grouting tunnel and a grout curtain were constructed in the middle part of the dam and extended the existing grouting tunnel and curtain in the right side of the dam finished in 2010. The total length of the grouting tunnel is 80 metres. It is of 1.8 meters wide and 2.5 meters high. The grout curtain reaches a depth of 36 meters. The works also include a drainage gallery which is 3.6 meter in diameter and installation of a system for monitoring the technical condition of the dam.