Coliform Enumeration in Potable Water, Dairy Water, Bottled Water and Vending Water Samples

PHL Location

Central Laboratory, Amite Laboratory, Lake Charles Laboratory and Shreveport Laboratory

CPT Code



MTT, Multiple Tube Fermentation 10-tube Most Probable Number (MPN) Technique for the Detection and Quantitation of Total and Fecal Coliforms in Potable Water.

Brief Description of Test

This method detects and estimates the total coliform population and the fecal coliform population in water samples through the use of sample inoculations into replicate tubes of selective media incubated under varying, well-defined conditions.

Possible Results

Total coliform & E. coli MPN/100 ml

Reference Range

<1.1/100 ml

Specimen Type

Potable water, Dairy Water (all types, including recirculated cooling water and glycol water), bottled water, vending water.

Specimen Container(s):

Sterile, disposable 100 ml Nasco Whirl-Pak bag containing a 10 mg sodium thiosulfate tablet; Bottled water-submitted in commercial packaging.

Minimum volume accepted:

100 ml

Collection Instructions

Collect representative sample according to established protocols. When using the Whirl-Pak bag fill to 100 ml line and leave at least 1 inch of air space at the top of container. Whirl bag to close. Do not twist tabs together.

Storage and Transport Instructions

Store refrigerated & transport sample(s) in clean cooler(s) with ice packs (ice is not recommended due to melting and possible cross contamination).  Submitters are encouraged to hold drinking water samples at <10ºC during transit. Dairy water samples must be 0 – 4.4ºC upon receipt in laboratory.  Maximum holding time is 30 hours.  Bottled water need not be refrigerated or cooled, and has no maximum holding time.

Causes for Rejection

Sample > 30 hours old; sample frozen, no sample ID, unacceptable collection container, insufficient sample, sample leakage, incomplete sample form, or sample totally immersed in ice-water.

Limitations of the Procedure

Improper mixing of sample will allow for underestimating of the bacteria density of the sample.

Interfering Substances

Excessive chlorine and heterotrophic levels.


  • Standard Methods For The Examination of Water and Wastewater, 18th Edition 
  • LA LDH-OPH Laboratory Services SOP DOLSOPDWM-03 Multiple Tube Fermentation 10 tube MPN Technique for the Detection and Quantitation of Total and Fecal Coliforms in Potable Water.

Additional Information

Complete a Lab 8 Laboratory Request and Report Form. The following is required Lab 8 information: Sample sequence #’s and project code, name of supply, collected by (name or initials), PWS ID (if applicable), date and time of collection, type of sample and disinfectant residual (if applicable).