This paper reports on our continuing work in optimizing microfiltration (MF) for water treatment and builds on previous publications. A more complete description of the findings and conclusions have been subject to peer-review and published elsewhere. The principal objective of this presentation is to compare MF fouling rates and filtrate water quality under conditions of constant flux and constant pressure operation. The implications for MF plant design, and operation will also be analyzed. Includes 11 references, table, figures.