The objective of this study is to develop and promote office automation system for water treatments, where object-oriented modeling techniques and relational databases are used. Functional dependencies can be used for specifying formally when a database design is good. In a relational database design of this study, the concept of embedded structure which satisfying complete functional dependencies is adopted. Tables similar to collections expedite the conversion process of relational databases to object-oriented databases. In this study, therefore, tables in relational data-bases are created so as to have a strong resemblance to collections in object-oriented databases.