DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Comparison showing the sectioned contents of a Brita water filter as purchased (left) and after six weeks of use in a house with copper pipes. The contents of the filter consist of a mixture of an ion exchange resin and activated charcoal particles. The resin removes some hardness from the water, as well as heavy metals such as lead and copper. The charcoal removes colouration of the water, and chlorine. The new filter is uniform in colour; the used one has zones of blue (top), white (middle) and brown (bottom, corresponding to unused). The blue colour is caused by copper being absorbed into the resin beads. In use, the water passes down the filter from the top.
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