Why is there a mysterious reddish-brown substance in the tap water of Westfield?

In the role of student chemists, students explore how new substances are formed as they investigate a problem with the water supply in the fictional town of Westfield. They analyze a reddish-brown substance that is in the water, the iron that the town’s pipes are made of, and a substance from fertilizer found to have contaminated the wells that are the source of the town’s water, and use their findings to explain the source of the contaminating substance.