Similarly, in 2011 the 70 μg/L WHO health-based drinking-water guideline for molybdenum was withdrawn with the assertion that molybdenum "occurs in drinking-water at concentrations well below those of health concern"; therefore, "it is not considered necessary to set a formal guideline value" [ 1].
However, two national-scale surveys of tube well water for other toxic elements revealed that As, manganese (Mn), uranium (U), boron (B), barium (Ba), chromium (Cr), molybdenum (Mo), nickel (Ni), and lead (Pb) are found at concentrations that exceed World Health Organization (WHO) health-based drinking water guidelines (BGS/DPHE 2001; Frisbie et al. 2002).
We then summarize the toxicity of these elements and review the rationale for WHO health-based drinking water guidelines.
In this study, we found concentrations of As, Cr, Mn, Ni, Pb, and U that exceeded WHO health-based drinking water guidelines.
For example, if the three tube wells that did not exceed WHO health-based drinking water guidelines for As, Mn, and U also did not exceed any other WHO health-based drinking water guidelines, they could supply safe drinking water to the residents of each neighborhood.
Well water in NB and other Maritime provinces commonly exceeds the health-based drinking water guidelines for Mn due to the underlying geology (New Brunswick Department of Environment and Local Government 2004).
The percentages of tube wells that had concentrations exceeding World Health Organization (WHO) health-based drinking water guidelines were 78% for Mn, 48% for U, 33% for As, 1% for Pb, 1% for Ni, and 1% for Cr.
For example, one tube well in Fulbaria, one tube well in Jamjami, and one tube well in Komlapur did not exceed WHO health-based drinking water guidelines for As, Mn, and U. Third, if a sample meets the WHO guidelines for As, Mn, and U, then it should be retested for Pb, Ni, Cr, B, Ba, and Mo.
In this neighborhood-scale study and in two national-scale studies of Bangladesh, levels of As, Mn, U, Pb, Ni, Cr, B, Ba, and Mo were above WHO health-based drinking water guidelines (Table 1) (BGS/DPHE 2001; Frisbie et al. 2002).
Since the WHO drinking water guidelines are supposed to provide adequate protection for all life stages, it is not clear why these age-weight based differences specified by the National Academy of Sciences were not taken into account by the WHO when establishing the drinking-water guideline based on the National Academy of Sciences 400 μg/day UL for adults.
According to WHO drinking water guidelines, total coliforms should not be detectable in any water intended for drinking (WHO 2006).
