This document describes a procedure for determining water hardness through titration with EDTA. Water hardness is defined as the calcium and magnesium ion content and is reported in parts per million (ppm) of calcium carbonate. The titration uses EDTA to chelate calcium and magnesium ions until the indicator Eriochrome Black T changes color, signaling the endpoint. Standard solutions of calcium carbonate and EDTA are prepared and used to determine the concentration of EDTA and calculate water hardness based on the volume of EDTA needed to reach the endpoint in a sample.