What is a significant characteristic of the most regulated contaminants in drinking water?

A significant characteristic of the most regulated contaminants in drinking water is that they can pose health risks primarily after long-term exposure. Many of these contaminants, such as certain heavy metals or chemicals, may not show immediate effects when consumed in small quantities. However, over time, cumulative exposure can lead to serious health issues, including cancer and organ damage. This characteristic emphasizes the importance of monitoring and regulating these contaminants to ensure long-term safety in drinking water supplies.

While some contaminants might be detectable in small amounts (as suggested in another option), not all regulated contaminants are constantly present in such detectable levels. Immediate treatment is not always required for all regulated contaminants, as some may be successfully managed through regular monitoring and treatment processes. Additionally, the assertion that they are non-toxic is inaccurate, as the very designation of these contaminants arises from their potential risk to human health.