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Environmental Microbiology

Water Microbiology

The State Public Health Lab tests drinking water for the presence/absence of coliforms and E. coli in compliance with the Safe Drinking Water Act. In addition, the laboratory tests surface or source waters, wastewater and runoff waters for indicator organisms and occasionally pathogens. Please call the laboratory before submitting or shipping water samples for analysis. However, it is not necessary to call the laboratory before submitting routine drinking water samples.

Specimen Collection and Shipment

Drinking water samples should be collected in sterile four-ounce whirl-pak bags or sterile collection bottles with sodium thiosulfate added to neutralize any chlorine in the water. Aseptically collect about 125 ml of water from the sample tap. If using the whirl-pak bags, be sure to whirl them closed tightly and tie the tabs together securely. Drinking water samples must be received and tested within 30 hours of collection. They can be hand carried or mailed to the laboratory to arrive the next day. Drinking water samples do not need to be iced during transit. Each sample must be accompanied by a properly completed Water Microbiological Sample Submission FormPDF. For compliance samples, the submitter must complete all bolded sections with an asterisk or the sample may be rejected.

Other water samples, such as surface water, source waters, runoff waters, etc. can be aseptically collected in any appropriate size sterile whirl-pak bag or bottle (sodium thiosulfate is not needed); however, at least 125 ml is needed to test. These waters need to be received in the laboratory within six hours of collection, and must be iced during transit. Since the transit time is so short, it is usually best to hand carry the water samples to the laboratory. A properly completed Water Microbiological Sample Submission FormPDF must accompany each sample. Before submitting these water samples, please call the Environmental Microbiology Department at (602) 542-6130 to arrange for testing.

Laboratory Analysis

Drinking Water Samples are routinely tested for the presence of total coliforms and E. coli using the enzyme substrate coliform test. This method provides results in 18 to 24 hours. The Standard Methods PA (Presence-Absence) coliform test is occasionally used, which provides results in 48 to 96 hours; both are EPA approved methods.

Other types of waters are tested for indicator organisms such as fecal coliforms, E. coli, fecal strep and enterococcus using either a Most Probable Number (MPN) method or a Membrane Filter (MF) method. The methods are Standard Methods. A list of methods is provided in the following table.

Method Name Units Standard Method Number Holding Time Matrix
Presence/Absence (P-A) Coliform Test Presence or Absence/100 ml SM 9221D 30 Hours Drinking, Well or Ground Water
Enzyme Substrate Coliform Test (Colilert/Colisure) Presence or Absence/100 ml SM 9223B 30 Hours Drinking, Well or Ground Water
Colilert Most Probable Number (MPN) (Colitray) MPN Index/ 100 ml SM 9223B 30 Hours 6 Hours Drinking, Well or Ground Water Surface/Ambient and Wastewater
Fecal Coliform Membrane Filter (MF) C.F.U/100 ml SM 9222D and SM 9221E 6 Hours Surface/Ambient and Wastewater
Standard Fecal Coliform Fermentation (15 Tube MPN) MPN Index/ 100 ml SM 9221B and SM 9221E 6 Hours Surface/Ambient and Wastewater
E. coli Determination (E.C. with MUG) C.F.U./100 ml Or MPN Index/100 ml SM 9221F 6 Hours Surface/Ambient and Wastewater

On occasion, waters are tested for pathogens, such as Salmonella. Please contact the Environmental Microbiology Department at (602) 542-6130 for these special requests.

Results and Reports

Results of Drinking water coliform tests are usually available within 18 to 24 hours after processing has begun. All positive results are called in to the submitter, providing that a telephone number has been supplied. Also, all compliance positive results and repeat samples are faxed to ADEQ. Leaked in transit and too long in transit samples are also called in to the submitter. Final reports will usually be mailed one to two days after initial processing. If the sample is checked as a compliance sample, a copy is sent to the submitter and ADEQ.

Other waters and their testing results are usually available within one to five days, depending on the method used and the target organism. Please call the Environmental Microbiology Department at (602) 542-6130 for an update at any time. Final reports are mailed to the submitter when all tests are completed.

Normally, the maximum contaminant level for total coliforms in drinking water is based on the presence or absence of coliform organisms in a 100-ml sample. A single water sample can have 0 coliforms per 100 ml. Other rules apply when more routine samples are collected, as the ADEQ compliance Department dictates. The number of samples required is based on the population served by a public water system. If a compliance sample is positive, repeat samples need to be collected. Please contact your ADEQ compliance officer to determine the number and location to collect these repeat samples.

The significance of the results of other waters and their tests depends on the circumstances. Consult with the laboratory and ADEQ if needed.