What common outdoor contaminant is monitored in water systems for safety?

The correct answer is pesticides because they are widely used in agriculture and horticulture and can enter water systems through runoff during rainfall or irrigation. Monitoring for pesticides is essential to ensure the safety and quality of drinking water, as many pesticides can be harmful to human health at certain concentrations.

In water distribution systems, maintaining safety standards is crucial, and the presence of pesticides can indicate potential contamination from surface runoff or improper pesticide application. Regulatory agencies set maximum contaminant levels for various pesticides, and monitoring helps to protect public health by ensuring that these levels are not exceeded.

While carbon dioxide and nitrogen oxides can impact water quality indirectly, they are not typically monitored as common contaminants in water systems. Oxygen levels (though important for aquatic life) are more related to the health of water bodies than direct contaminants impacting drinking water safety. Thus, pesticides are the primary concern within the context of outdoor contamination that directly affects water systems.