Two organic molecules that give fresh water an earthy taint are perfectly harmless but undesirable to many people. Now, Australian scientists have discovered that old sand filters with an active biological film are much more effective at breaking down these molecules, geosmin and methylisoborneol (MIB), than new filters with no biofilm. According to Gayle Newcombe, Research Leader at the Applied Chemistry Unit of the Australian Water Quality Centre in Salisbury, South Australia, "Although adverse odors do not present a risk to human health, their presence often leads to a misconception that the water is unsafe for drinking." Geosmin is also familiar to many people as the earthy smell of rain it is itself a bacterial natural product.
Filtering earthy water