For an average 2-year-old, how much does water contribute to their lead exposure?

The correct answer highlights that for an average 2-year-old, water contributes significantly to their lead exposure, specifically in the range of 5-50%. This understanding is crucial because young children are particularly vulnerable to the effects of lead, and identifying sources of lead exposure allows for better preventive measures.

Water can be a notable source of lead if it has been distributed through lead pipes or if the plumbing system contains lead-based materials. Since young children tend to have higher rates of exposure due to their behaviors—such as putting their hands or toys in their mouths, and their tendency to consume large amounts of fluids relative to their body weight—it's important to account for water as a potential source of lead in their environment. The broader range provided by this answer reflects the variability in lead concentration in different water supply systems, highlighting that while water can be a significant contributor, the level can vary widely depending on specific circumstances.

The other answer choices do not capture the full range of possible exposure from water, underselling the potential risks faced by young children living in environments where lead may leach into their drinking water. In some scenarios, the contribution could indeed be higher than what the narrower ranges suggest, emphasizing the need for thorough testing and monitoring.