Contamination and pollution are a running motif throughout An Enemy of the People. This motif begins when Thomas Stockmann discovers the literal contamination of the Baths; what was meant to be a source of purifying medicinal water is instead responsible for several illnesses among the Baths’ initial clients. Since the contamination consists of invisible microbes, many people do not believe Thomas’s claims. The water appears to be clear, so they assume it must be pure, and Thomas must be mistaken. Morten Kiil, whose tannery bears primary responsibility for the contamination, epitomizes this skepticism. He refers to the bacteria dismissively as “beasts” and “little animals,” strongly implying that what he cannot see with his own eyes must be imaginary.

Soon, the contamination of the water becomes a metaphor for the political situation in the town; everything appears well run on the surface, and citizens are generally satisfied, but people like Hovstad and Petra see that a few wealthy people are making all the decisions and that many of their choices are misguided. At first, many of the characters agree that this “pollution” should be addressed. Hovstad, Billing, and Petra yearn for revolution from the beginning, and Thomas begins to agree with them after he realizes that Peter cares more about money than about keeping the town safe.