Often, the reason is very a low hardness: if drinking water is very soft, it usually is very agressive. This has no effect on stainless steel and plastic pipes, but in pipes made of other materials, it can cause surface corrosion. Corrosion can also be caused by the interaction of various natural water constituents, foreign particles that have been washed in and oxygen. Branched pipe installations with low water movement and “mixed installations” favour rust formation. This rust in turn colours the water brown.