What is the primary cause of red staining on pipes?

The primary cause of red staining on pipes is indeed iron. When iron is present in water, especially in the form of dissolved ferrous iron, it can oxidize and form rust (ferric oxide), which gives a characteristic red or reddish-brown color. This staining can occur in both ferrous mains and in plumbing systems where iron pipes are used.

The conditions that lead to this red staining are often related to corrosion of iron pipes, with acidic or low-oxygen environments exacerbating the situation. Additionally, the presence of microbial activity can promote corrosion, resulting in the release of iron particles into the water supply, contributing to the staining of fixtures and surfaces.

Manganese can also cause staining but typically manifests as black or brown deposits rather than red. Lead and copper do not typically cause reddish stains; lead can leach into water but is more associated with a white or bluish discoloration in some cases, while copper tends to turn blue or green due to corrosion. Therefore, iron stands out as the primary culprit behind red staining in plumbing systems.