The pH value of tar waters from the Kiviter retorts depends, first of all, on the dust carry-over with oil vapours and gas from the retorts. This dust contains free calcium oxide that initiates alkaline reaction of tar water. The recommendations for diminishing the dust carry-over are presented: lowering the temperature in gas outlets; using four gas outlets for 1000 t retorts; transition to the use of low-concentrated oil shale, processing oil shale in circular retorting chamber, etc.