A study was undertaken to determine the characteristics of municipal applications in which filter aid filters may be used sucessfully, to study the effect of various variables on filtration economy and effectiveness, and to outline a procedure for designing a plant to operate with maximum economy. A digital computer program has been prepared to develop a filter cake resistance prediction equation from the results of several filter runs conducted with different levels of suspended solids and/or body feed. The paper describes in brief the required MAIDS Manipulation and interpretation of data systems) program listed in Fortran language, and describes its use with several examples.