A water chamber for a respiratory therapy apparatus has a base casing, a cover casing and a partition. The partition makes the air flows downward, turns around and then goes up to prolong the route and the time of the air passing through the water chamber. Therefore, the air can be saturated with moisture sufficiently to increase the air humidity. When the air is passing through the water chamber, the air is divided into two parts to each respectively enter a first tube and a second tube. The audio frequencies caused by the two parts of the air are changed due to a change of a cross sectional area. When the two parts of the air converge, the audio frequency is changed again. The partition makes the air in different portions of the water chamber have different audio frequencies, thereby reducing the resonance to eliminate noise.
