An inspection made at the Winnetka water filtration plant on February 20, 1936, showed ice thickness of 20 inches at the inlet and 22 inches at the outlet of the 15 foot depth open coagulating basins; 4 inches thick in the partially-enclosed concrete, rapid sand filters; and 7 inches thick at the outlet of the enclosed finished water reservoir. Freeze-up conditions on the distribution system also existed at the same period. To assist in overcoming the problems encountered during the unusually cold weather, the discharge from the adjoining municipal power plant condenser equipment was used for raising the temperature of the raw water supply at the water filtration plant. The power plant condenser equipment (figure 1) used for a 2500kilowatt turbo-generator, consists of a cooling pond with approximately 900,000 gallons capacity at 3J feet average depth, 340 foot length by 100 foot and 132 foot widths; a recirculating pump, motor driven, centrifugal type, 5800 G.P.M. capacity, operating at 7.0 M.G.D. rate at period of raising temperature of raw water supply; and a surface condenser of 4700 square feet tube surface. The cooling pond is divided into two sections by a sheet piling wall having 3 sluice gates to by-pass the water from one section of the pond to the other for water temperature control. At the time of by-passing condenser water to the water plant intake, number 1 gate in cooling pond was wide open, number 2 gate was closed, and number 3 gate was wide open. Raising the temperature of the raw water supply was done by opening the valves on the by-pass line from the condenser discharge line to the water plant intake pipe, and having the condenser discharge line valve (located at the cooling pond) in open position. The water flow under these circumstances is from the cooling pond