The proposed revised Part H2, of the Building Regulations (England and Wales), and the proposed new Part M of the Technical Standards for compliance with the Building Standards (Scotland) Regulations 1990, as amended, both make reference to reed bed systems for treating domestic wastewater. This Guide provides guidance to support building regulation requirements, describing typical applications and current accepted minimum design specifications for reed beds treating settled domestic wastewater. Part 1 of this Guide describes the historical development of the various reed bed systems along with some of the current variations in design. It also covers the expected performance of such systems, and their application.