Determination of Total and Temporary Hardness in Waters of Differing Origin and Treatment by EDTA Complexometric Titration: Implications for Soil and Agricultural Water Use

Abstract

Water hardness, the combined concentration of dissolved calcium and magnesium ions, affects drinking-water taste, soap performance, and the formation of scale in heating equipment. In this study, total hardness was determined by direct complexometric titration with 0.01 M disodium EDTA at pH 10, using Eriochrome Black T (EBT) as the indicator. Six water types were analysed: distilled water, rain water, reverse-osmosis (RO) water, household drinking water, commercial bottled drinking water, and boiled tap water. Each 100 mL sample was buffered, indicated, and titrated to the pink-to-violet-blue endpoint, giving a direct conversion of 0.1 mL EDTA to 1 ppm as CaCO₃. Total hardness ranged from 1.2 ppm (lowest sample) to 142 ppm (highest sample). Comparing boiled and unboiled tap water gave a temporary hardness of 78 ppm (54.9% of total). All six samples were below the BIS acceptable limit of 200 mg/L. The results show that water source and treatment (distillation or RO versus mineral-bearing supplied water) have the strongest influence on hardness, and that the method is a low-cost, reliable way to screen water quality with basic school or college laboratory equipment. Because Ca²⁺ and Mg²⁺ also control irrigation-water quality, soil structure and the performance of sprayed agrochemicals, the results are converted to meq/L and interpreted for agricultural use, as a water-side companion. Hardness alone cannot establish irrigation suitability, which also requires sodium, bicarbonate and salinity data; the study therefore frames, rather than answers, the question of whether the hardness of the water used to prepare and apply fertilisers affects their performance