Table 2. Mean metal concentrations, two water supply schemes, Nigeria, 2010–2011.

Location sampled	Mean upper 95% CI limit of concentrationa (mg/l)
	Cd	Co	Cr	Mn	Pb
Asejire water supply scheme
Consumer tap waterb	0.06	0.08	0.23	0.10	0.25
Treatment works	0.01	0.08	0.25	0.13	0.18
Dam water	0.20	0.19	0.34	0.43	0.49
Eleyele water supply scheme
Consumer tap waterb	0.04	0.09	0.12	0.23	0.31
Treatment works	0.02	0.09	0.12	0.24	0.29
Dam water	0.43	0.17	0.43	0.54	0.66
WHO MCL1	0.003	0.10c,d	0.05	0.04	0.01

Cd, cadmium; CI, confidence interval; Co, cobalt; Cr, chromium; MCL, maximum contaminant level; Mn, manganese; Pb, lead; WHO, World Health Organization.

^a The mean annual upper 95% confidence interval (CI) limit for the concentration was calculated from the mean upper 95% CI limit of the concentration in the dry season (C_d) and the mean upper 95% CI limit of the concentration in the wet season (C_w) by assuming that the dry season lasted 4 months and the wet season, 8 months and using the formula: ((C_d × 4) + (C_w × 8))⁄12.

^b The mean upper 95% CI limit of the concentration in consumer tap water during the wet and dry seasons was calculated by averaging measurements in all supply areas for a particular scheme during the respective season.

^c Maximum contaminant level from the environmental media evaluation guide for children (California Department of Public Health).¹¹

^d Maximum contaminant level from health-based groundwater quality criteria (New Jersey Department of Environmental Protection.)¹²