Explanation

Blue Baby Syndrome (infant methemoglobinemia) is caused by nitrate contamination of drinking water, typically from fertilizer runoff, animal waste and sewage. In the infant's gut, bacteria convert the ingested nitrates into nitrites; the nitrites oxidize the iron in haemoglobin from Fe(II) to Fe(III), forming methemoglobin, which cannot carry oxygen. The resulting oxygen deprivation turns the baby's skin bluish. The question asks about the contamination of the water supply, which is nitrate — sulphites and sulphates play no role in this condition.