record coliform concentration as MPN/100 ml. MPN values for a variety of positive and negative tube combination are given in a tables 9221:II, and IV the sample volumes indicated in tables 9221:II,III are chosen especially for examining drinking water. tables 9221:VI illustrates MPN values for combinations of positive and negative results when five 10 ml, five 1.0 ml, five 0.1 ml sample portion volumes of non-potable water are tested. If the sample portion volumes used are those found in the tables, report the value corresponding to the number of positive and negative results in the series as MPN/100 ml. when the series of decimal dilutions is different from that in 9221: IV, select the MPN value from table 9221:IV for the combination of positive results and calculate according to the following formula: