A good quality drinking water is essential for human survival. However, a large percentage of the populations in most developing countries (Nigeria inclusive) do not have access to potable water. This study was therefore conducted to assess the extent of risk arising from consumption of toxic elements in groundwater samples collected from Lagos and Ogun States, Southwest, Nigeria. Twelve toxic elements concentrations (As, Mn, Cd, Cr, Pb, Ni, Al, Ti, V, Hg, Li, and Sn) were determined from 170 groundwater samples using inductively coupled plasma-mass spectrometry, and the physicochemical parameters were determined using standard methods. The pH results revealed that most of the water samples were slightly acidic. Of the twelve toxic elements, only Mn, Cd, Pb, Ni, and Al have concentrations higher than the WHO recommended limit in drinking water. The average dose of Mn and Al consumed daily from groundwater by an adult in Lagos state is 3.4 and 23.2 (μg/kg body weight), respectively. Similarly, an adult in Ogun State consumed an average daily dose of 6.09 and 25 (μg/kg body weight) Mn and Al, respectively. A greater threat was posed to children and infants. The order for risk of cancer in groundwater from Lagos State was Pb > Cr > As > Cd while the order in Ogun State groundwater was Cr > Cd > As > Pb. The relative high concentrations of Mn, Al, and Pb obtained in this study can be attributed to industrial and anthropogenic activities in the study area. Treatment of groundwater before consumption is recommended to avoid possible adverse cumulative effect. Improved waste disposal methods and regular monitoring of toxic elements in groundwater of the study area should be adopted to safeguard human health.

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This study focused on designing a drinking water systems sustainability index for Integrated Water Resources Management in low-income countries. Water Supply Systems Sustainability Index (WSSI), a field assessment tool, was designed for rapid appraisal of drinking water systems in selected urban, peri-urban and rural Nigerian communities. The systems were classified into Highly Sustainable, Sustainable, Averagely Sustainable, and Unsustainable WSSI categories. Sanitary Risk Score (SRS) was assigned, classifying drinking water systems into Very High, High, Intermediate (Medium) and Low-Risk categories. WSSI results revealed that for urban systems, 90 are Highly Sustainable, 27 are Sustainable and 12 are Averagely Sustainable. For peri-urban systems, 13 are Highly Sustainable, 7 Sustainable and 1 Averagely Sustainable. Only urban hand-dug wells are in the Very High-Risk category. Public water supplies occurred only in the Low-Risk (17) and Intermediate-Risk (6) categories. Urban and rural boreholes had better quality than peri-urban boreholes. WSSI and SRS correlation result indicated strong positive correlation for urban hand-dug wells' (R2 = 0.5688, at p < 0.05) and weak positive correlation between peri-urban hand-dug wells' (R2 = 0.1847, at p < 0.05) and urban boreholes' WSSI and SRS (R2 = 0.2032, at p < 0.05). Findings showed that drinking water systems are, generally, sustainable and WSSI could be incorporated into community-level water supply assessment.

A quantitative evaluation of spatial and temporal distribution of groundwater recharge is a prerequisite for the management of ground water resources system in an optimal manner. The amount of groundwater recharge depends upon the rate and duration of rainfall, as rainfall is the principal means for replenishment of moisture in the soil water system and recharge to ground water. This paper investigated the relationship between rainfalls and groundwater recharge within Ona River basin, southwest Nigeria, using soil moisture balance and water table fluctuation. Analysis of rainfall trends within the Ona River basin suggests that there is considerable high annual rainfall occurrence, with a mean of 1623.48. It must be noted that the mean annual lost due to evapotranspiration of 1361.68 mm is very high when compared to the rainfall (83.9%). The results obtained from the soil moisture balance when considering the three dominant soil types within the basin, that is, sandy loam, clay and find sand, having water capacity of root zone value of 70, 70, and 50 respectively, suggests that groundwater recharge follows a positive trend as the corresponding rainfalls. However, empirical relationships of: y = 0.540x-606.2, with a coefficient of determination (r 2) value of 0.719, for sandy loam and clay; and y = 0.552x-621, with a coefficient of determination (r 2) value of 0.726 for fine sand was established for the basin area. On the other hand, recharge ranging from 220.25 to 40.50 mm was computed from the water table fluctuation method.

Low-quality mine water from collieries may be used in large quantities to irrigate agricultural crops on virgin (unmined) and rehabilitated soils in South Africa. Such a use could enhance crop production and allow environmentally sustainable mine water disposal. In this study, the volume and qualities of the runoff from two centre pivots irrigated with moderately saline mine water, as well as their soil water salinities, were monitored and used to determine water and salt balances, using the modified ACRU agrohydrological model, ACRU2000, and its salinity module, ACRUSalinity. At both sites, much of the water evaporated, while a significant part of the salt input either precipitated or remained with the water in the soil horizons. A higher percentage of drainage water (and salinity) were retained as ground water storage and a lower percentage of runoff occurred in the rehabilitated sandy loam soil, while a higher percentage of salts accompanied runoff in the virgin clayey soils. Simulated salt saturation values indicate that many crops could be successfully irrigated at 100% yield potential at either site. Electrical resistivity surveys were carried out at both sites. A general decrease in resistivities with depth in both the virgin and rehabilitated soils reflected the decreasing influence of the mine water used for irrigation with depth and the precipitation of salts in the soils close to the ground surface. The occurrence of a thicker, low-resistivity, near-surface layer near the exit of each pivot area indicates that the water and salt content of the subsurface increased in the direction that the surface and nearsurface irrigation water flowed.