Abstract: A continuous flow condensation particle counter employs a working fluid to saturate a gas stream, and then condense onto particles carried in the gas stream as the stream is directed through a condenser and cooled below the supersaturation point. A porous saturation block is positioned beneath the condenser, and receives droplets of working fluid condensate and water as the droplets descend from the condenser by gravity. The saturation block is constructed of a hydrophobic material, whereby it allows the working fluid to pass through but retains water within a collection reservoir centered below the condenser. A vacuum pump and a periodically actuated solenoid valve are employed to introduce a partial vacuum to the reservoir and thereby evacuate accumulated water. The preferred working fluid is a perfluorinated hydrocarbon fluid that is substantially odorless, chemically inert and non-flammable. Water is immiscible in the working fluid, and thus readily separable.