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Bacteriological Laboratory



Photos of Water Samples.

The Water Microbiology Laboratory performs bacteriological analyses on water samples submitted by water system collectors, Office of Drinking Water and private citizens for well water analysis. The Bacteriological Laboratory examines for the presence of indicator organisms and pathogenic bacteria that maybe present in public and private drinking water samples. Testing processes used for presence/absence and quantitation are Environmental Protection Agency approved methods.

The Delaware Public Health Laboratory (DPHL) utilizes the IDEXX Colilert Test, for the presence/absence of total coliforms, using proprietary Defined Substrate Technology (DST) to simultaneously detect total coliforms and E. coli. Two nutrient-indicators, ONPG and MUG, are the major sources of carbon in Colilert and can be metabolized by the coliform enzyme β-galactosidase and the E. coli enzyme β-glucuronidase, respectively.

As coliforms grow in the Colilert Test, they use β-galactosidase to metabolize ortho-Nitrophenyl-β-galactoside (ONPG) and change it from colorless to yellow.


Environmental Bacteriology.

E. coli use β-glucuronidase to metabolize beta-Glucuronidase (MUG) and create fluorescence. Since most non-coliforms do not have these enzymes, they are unable to grow and interfere. The few non-coliforms that do have these enzymes are selectively suppressed by the Colilert Test's specifically formulated matrix.


Environmental Bacteriology.


This approach is different from traditional media, which provide a nutrient-rich environment that supports the growth of both target organisms and nontargets. When nontargets grow and mimic target organisms, false positives occur. Growth of nontargets can also suppress target organisms and give false negatives in traditional media. To suppress nontargets, traditional media often include high levels of salts, detergents, or other selective agents that may inadvertently suppress target organisms and give further false negatives.*

Public water system reports are submitted to the Office of Drinking Water. Private well sample reports are mailed to the corresponding County Health Unit and the Health Unit will in turn mail the report and brochure to the customer. As an EPA State Primacy Water Laboratory, the DPHL is the enforcement authority responsible for ensuring that public water systems comply with the Safe Drinking Water Act.

*information was referenced from the IDEXX website


Drinking Water Tests at the Delaware Public Health Laboratory

Approved Drinking Water Analytical Methods | Methods Approved to Analyze Drinking Water Samples to Ensure Compliance with Regulations | US EPA

National Primary Drinking Water Regulations including Maximum Contaminant Levels | Ground Water and Drinking Water | US EPA

Safe Drinking Water Search for the State of Delaware

Types of Drinking Water Contaminants | Drinking Water Contaminant Candidate List (CCL) and Regulatory Determination | US EPA

Drinking Water Requirements for States and Public Water Systems | US EPA


More information about drinking water testing

Public Water Supply

Private Well Owners

Drinking Water Public Notices

Private Drinking Water Forms


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Return to the Delaware Public Health Laboratory home page.



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