Is there iron in your water?
In some cases, tap water may contain iron residues from rust in the metal pipes through which it flows. Some of the iron of which the pipes are made is dissolved in the water and gives it a reddish-brown colour.
This phenomenon may also be due to water that is naturally ferruginous or rich in iron, because of the type of rock through which it passes. Although the iron is not bad for your health in moderate quantities, it gives the water a metallic taste and may stain clothes during washing.