What water constituent is associated with staining plumbing and clothing dark brown or black?

The presence of manganese (Mn) in water is known to cause staining of plumbing fixtures and clothing, resulting in a dark brown or black coloration. Manganese can enter water supplies from natural deposits in the earth or through industrial discharges. When water high in manganese content comes into contact with oxygen, it can precipitate, leading to the dark stains that are often found on sinks, bathtubs, and laundry.

Manganese is not only of aesthetic concern; elevated levels can also pose potential health risks if ingested over long periods. This makes it important for environmental health specialists to monitor and manage manganese levels in drinking water supplies to prevent staining and health risks.

The other options, while they may also be associated with water quality issues, do not cause the dark brown or black staining characteristic of manganese. For instance, zinc can impart a bluish tint but is less likely to cause staining of that nature, while silver can cause a grayish or bluish stain but does not lead to the distinctive dark discoloration associated with manganese. Calcium, on the other hand, is primarily responsible for hard water and scale buildup, rather than coloration or staining.