To protect population against waterborne diseases many water treatment plants use the Fermentation Tube Test (FTT) to assess bacterial pollution of raw water. This simple monitoring technique is based on repetitive sampling of water with a set of standard tubes, followed by adding lactose to the water samples and counting samples from which fermentation gas is released. Gas that results from lactose consumption by bacteria can be easily detectable, which makes the FTT an attractive measuring technique. Number of fermenting tubes is a basis for calculating the Most Probable Number of bacteria (MPN), classical measure of bacteriological content in water. It seems that little has changed from the time when well known article on MPN was published by Cochran .