What common water source might pose a risk of nitrate contamination for infants?

Well water is recognized as a common water source that might pose a risk of nitrate contamination, particularly for infants. This is primarily due to the fact that well water can be influenced by agricultural practices, which often involve the use of nitrogen-based fertilizers. When these fertilizers leach into the groundwater, they can lead to increased nitrate levels. Infants are particularly vulnerable to high levels of nitrates, as this can lead to a condition known as methemoglobinemia, or "blue baby syndrome," which impairs the blood's ability to carry oxygen.

In contrast, other sources such as tap water, rainwater, and mineral water generally undergo various treatment processes or have fewer direct contaminant sources that exacerbate nitrate levels, making them less likely to pose such a significant risk for infants when compared to well water. For example, municipal tap water is treated and regulated to meet safety standards, and rainwater is typically less exposed to agricultural contaminants. Thus, well water remains a primary concern for nitrate contamination in infants due to its potential origins and lack of regulation compared to other sources.