The American Concrete Institute Committee 350, Environmental Engineering Concrete Structures, recognized a need for standardized criteria as well as a standardized method of testing reinforced concrete structures for watertightness. AWWA's Committee 400, Waterproofing, was also interested in documenting the state-of-the-art watertightness testing and criteria for reinforced concrete tanks. A joint subcommittee was subsequently formed to prepare a report containing recommendations on watertightness for reinforced concrete containment structures. This article presents the findings of the joint report. Includes 4 references, table.