This document is an instructional module package prepared in objective form for use by an instructor familiar with hardness analysis using the EDTA method and the calculation of hardness given metal ion concentrations and a factor table. Included are objectives, an instructor guide, student handouts, and transparency masters. A video tape is also available from the author. This module considers principles of hardness, calculation of hardness, preparation of reagents for the EDTA method, calculation of results and interferences and inhibitors. (Author/RH)