Louisiana Department of Health & Hospitals | Kathy Kliebert, Secretary

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Detection in potable, dairy, bottled and vending water samples


PHL Location

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

CPT Code



Colilert 18, Colilert 24, Colilert test, potable water test, MMO-MUG Presence Absence; Chromogenic Fluorogenic Substrate Method; SM9223

Brief Description of Test

Primary water test that simultaneously detects total coliforms and E. coli using Defined Substrate Technology.

Possible Results

Total coliforms & E. coli “Present” or “Not found”.

Reference Range

Total coliforms & E. coli “Not found”.

Specimen Type

Potable Water; Dairy Water, Bottled Water; Vending Water.

Specimen Container(s):

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

Minimum volume accepted:

100 ml

Collection Instructions

Potable water samples are collected in sterile, approved containers, containing sodium thiosulfate. The most commonly used collection containers for potable water are sterile disposable 100ml Nasco Whirl-Pak bags, each containing a 10 mg sodium tablet. The sampling container must remain closed to maintain sterility until the time that the sample is collected. When the sample is collected, ample air space (at 1 inch) must be left at the top of the container to facilitate mixing of the sample by shaking. When using the 100ml Nasco bag, the bag should be filled to the 100ml fill line mark on the bag and leave at least 1 inch of air space at top of container.  Whirl bag to close.  Fold tab ends down. 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; Frozen water sample; No sample ID; Unsatisfactory collection container; insufficient amount of sample; sample container leaking;  sample information form not complete.  

Limitations of the Procedure

Not suitable for marine water or any sample altered by any pre-enrichment or concentration. Colilert 18 hour test not approved for Dairy Waters. Not suitable for source water, surface water, or wastewater as these require enumeration of organisms.

Interfering Substances

Excessive Chlorine; Samples containing humic material with innate color.


Idexx Laboratories Colilert, Colilert 18 package inserts; LA DHH-OPH Laboratory Services SOP DOLSOPDWM-01 Chromogenic Fluorogenic Substrate Method.

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, Date/Time Collected. Type of Sample.