Which mineral commonly found in water can discolor bathroom fixtures?

Iron is the mineral that commonly causes discoloration in bathroom fixtures when found in water. When water contains high levels of iron, it can oxidize and lead to rust, resulting in reddish-brown stains on sinks, bathtubs, and toilets. This discoloration can be particularly noticeable in areas that are frequently wet, leading to maintenance challenges for housekeeping staff.

Calcium and magnesium can also be present in water, contributing to hardness, which may cause scale buildup but typically does not result in discoloration similar to iron. Iodine, while it can be found in some water supplies, is not a common cause of discoloration in bathroom fixtures. Therefore, iron is specifically recognized for its tendency to stain and discolor surfaces, making it the correct answer in this context.