Colour in water (after it has been filtered) is typically caused by both iron and manganese compounds or by organic compounds. If the colour is due to iron or manganese there are specific treatments (see the iron and manganese data sheets). If the colour is due to organics then treatment is normally by ion exchange or activated carbon. Organic colour comes from decaying vegetation and may be completely soluble or particulate. Tannins (Humic and Fumic acids) are by far the most common class of compounds and give the water a yellow/brown tint. In highland areas where water runs off peat the water can be virtually brown.