**3.7 Hardness**

The hardness recorded in this study ranged from (22 to 132) mg/l as shown in **Table 4** with a mean value range of (73.33 to 105,67)mg/l as shown in **Table 5** during the rainy season and the value range of (48 to 187)mg/l as shown in **Table 2** with a mean value of (117 to 153)mg/l as shown in **Table 3** during the dry season. In this study only three sampled sites KL3,(48 mg/l), SD1(67 mg/l) and SB1(90 mg/l) recorded hardness within the WHO permissible limit of 100 mg/l. The remaining sampled sites are above the WHO (100 mg/l) permissible limit while during the rainy season, fifteen of the sampled sites water hardness ranged from(22 to 97)mg/l as shown in **Table 4** are within the WHO permissible limit of 100 mg/l and twelve of the sampled sites water hardness ranged from(102 to 132)mg/l are above the WHO permissible limit of 100 mg/l These high values could be due to the high concentrations of dissolved salts such as MgSO4, CaSO4, CaCO4 found in rocks and soils. Most commonly associated with the ability of water to precipitate soap. As hardness increases, more soap is needed to achieve the same level of cleaning due to the interactions of the hardness ions with the soap. Chemically, hardness is the sum of polyvalent caution concentrations dissolved in water. In fresh waters, the principal hardness-causing ions are Calcium and Magnesium; Strontium, Iron, Barium and Manganese ions also contribute. The hardness recorded in this study range from 48 mg/l – 187 mg/l (**Table 4**), and a mean value of 117 67.09 mg/l – 153.3 30.35 mg/l. This is above the mean hardness range of 45.5 4.79 mg/l – 105.0 46.74 mg/l reported by Dimowo [22] in an assessment of some physicochemical parameters of River Ogun (Abeokuta, Ogun State, Southwestern Nigeria) in Comparison with National and International Standards. These values exceed the maximum permissible WHO standards of 100 mg/l. this could be due to high concentrations of dissolved salt such as MgSO4, CaCO3, found in rocks and soils.
