<p>come to think of it, this might also partly explain the common practice of putting lemon in water.</p><p>geosmin is remarkably difficult to remove from water supplies (if you treat it with an acid, you need to get the acid out again, and once the water is back to neutral the geosmin will reappear due to constant production by harmless bacteria, and humans can detect it at parts-per-billion levels) and in some areas of the world it causes problematic levels of taste and odour.</p>