Household water is subject to special protection, as confirmed by the number of evaluated parameters, of which hardness and magnesium content deserve special attention. On the other hand, although calcium is not a limiting constituent although its concentration as well as the calcium compounds affect water hardness. Therefore, calcium is an element which is usually determined in raw water, after treatment as well as at the enduser. For hygienic reasons, particular attention is paid to magnesium concentration in water as well as quantitative relations between Mg and Ca. The aim of the study was to determine water hardness and the content of calcium and magnesium in treated water intended for consumption by residents of the town of Leszno. The investigations were carried out in 2006-2009 on water samples derived from three water intakes and a water treatment plant.  Water samples were collected in accordance with the PN-ISO 5667 standard and the aforementioned parameters were determined with the assistance of the ethylene diamine tetraacetic acid (EDTA) method (PN-ISO 6059). Total hardness of the examined waters ranged from 192.0 to 410.0 mg CaCO3 dm–3, averaging 334.9±33.16 mg CaCO3 dm–3. The above values, despite apparently high extreme ranges with respect to mean values, were similar between the examined intakes and years, not showing any statistically significant differences. Calcium concentrations in the examined waters ranged from 24.7 to 152.4 mg dm–3, on average 73.46±31.15 mg dm–3, while those of magnesium from 1.6 to 107.1, on average 20.45±27.77 mg dm–3. It is evident from the analysis of the experimental data that the overall hardness of the examined waters failed to correlate with calcium and magnesium concentrations. On the other hand, positive correlation was observed between calcium and magnesium concentrations. It was also concluded that, after treatment, household water in Leszno met the qualitative requirements of the examined parameters. The recorded mean water values showed that household waters in Leszno can be described as moderately hard of lowered magnesium concentration.