Abstract: A piping arrangement for an air washer is disclosed which enables the air washer to maintain constant dewpoint of air passing from the leaving side of the air washer. Chilled water is sprayed from a first manifold and is used to cool air to a required wet bulb temperature. The air is then passed through subsequent manifolds having spray nozzles which further humidify the air until the air reaches a required dewpoint temperature in a substantially saturated state.