Water hardness is defined as the soap-consuming capacity caused by dissolved Ca2+ and Mg2+ ions. This experiment employs a three-titration EDTA strategy to resolve total hardness into its temporary (carbonate-based, removable by boiling) and permanent (chloride/sulphate-based, requiring chemical treatment) components. EDTA (Na2H2Y) forms stable 1:1 chelate complexes with both Ca2+ and Mg2+ at pH 10, maintained by an ammonia/ammonium chloride buffer. Eriochrome Black-T (EBT) is the indicator: it forms a wine-red complex with the metal ions that is displaced at the end point as EDTA takes over, producing a clean steel-blue colour. The experiment begins with standardisation of the EDTA solution against Standard Hard Water (1 mg CaCO3/mL). Three titrations follow: total hardness on the raw sample, permanent hardness on the boiled-and-filtered sample, and temporary hardness by subtraction. Results are reported in ppm CaCO3 and converted to French, Clark, and German degrees. The engineering consequences of each hardness category are discussed: CaCO3/Mg(OH)2 scale reduces boiler heat-transfer efficiency, and high-pressure boilers require feed water below 50 ppm.