Technologies appropriate for use by developing country communities in designing water treatment plants for public water supplies are presented in this report, which advocates the design of low-cost, labor-intensive plants using indigenous resources. After a chapter on considerations to be addressed prior to designing the plants, the report discusses appropriate technologies in regard to pretreatment, chemicals and chemical feeding, hydraulic rapid mixing, hydraulic flocculation, sedimentation, and filtration. Succeeding chapters present standardized designs, particularly those pertaining to package and modular plants, and review pertinent cost data. A final chapter examines the human resources needed to operate and maintain developing country water treatment plants and considers related training requirements; the more valuable and proven technologies are summarized at the chapter's end. The text contains 51 tables and 128 figures. Material on chemicals, hydraulic calculations, and simple methods for water analysis, together with a checklist for design and a glossary of organizations to which inquiries for related information can be addressed, are included in the appendices. A selected bibliography (14 entries, 1959-82) and a list of references (143 entries, 1927-82) conclude the manual.