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Regarding the nitrates issue see my previous email on nitrates. The emergency issue is short term risk to bottle fed babies, especially with gastro-intestinal infections. Babies taking in lots of high nitrate water (used for making up bottled milk) run greater risk of the bacteriological reduction of nitrate to nitrite (especially due to high bacterial loading during gastro-intestinal infections) and the nitrite blocking the oxygen transfer in haemoglobin. The risk is blue baby syndrome even over a short period. Targeting mothers with infants and pregnant mothers with a different source of water or promoting breast feeding and strong hygiene measures should negate this risk. Other emergency risks are minimal.
It is the combined figure of nitrites and nitrates that is the risk as nitrates reduce to nitrites which cause the problem. If the combination of ratios of tested nitrites to acceptable nitrites (3mg/l) and tested nitrates to acceptable nitrates (50mg/l) are above one then there is a risk to bottle fed babies. With water tested at above 50mg/l nitrates, and unknown nitrites it is better to try to provide other sources of water to pregnant women and mothers with young babies (who bottle feed).
Other possibilities are to blend the water with other sources of lower nitrate/nitrite concentrations. WHO says that a minimum is to ensure the water is well disinfected with a residual so that the bacteriological loading is minimal and therefore reduction of nitrates to nitrites is minimised. Better still is to provide other water sources to the bottle fed infants and mums.