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Water microbiology testing laboratories are increasingly looking
for methods that provide accurate quantitative results. A large part
of microbiology testing involves drinking-water testing in compliance
with the U.S. EPA’s Total Coliform Rule (TCR). To comply with the TCR,
many laboratories complete tests that determine the presence or
absence of total coliform bacteria and E. coli in a 100-mL
sample. It is now becoming more common for laboratories to conduct
quantitative testing in addition to presence/absence testing.
Recent regulatory changes have spurred an increase in
quantitative water testing. In July 2003, the U.S. EPA published the
Ambient Water Rule (40 CFR Part 136) in which both recreational and
source waters are defined as ambient water. The Rule specifies E.
coli and enterococci bacteria as the best indicators of fecal
contamination in these waters. The Long Term Stage 2 Enhanced
Surface Water Treatment Rule (LT2) asks drinking-water providers to
measure E. coli and Cryptosporidium in their
source waters. |
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In the Ambient Water Rule, the U.S. EPA specifies that E. coli and enterococci
are the best indicators of fecal contamination in ambient water.
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The U.S. EPA is expected to promulgate this rule in January, 2006. On
August 16, 2005, the Proposed Wastewater Rule (40 CFR Part 136) was
published, which specifies test methods for the enumeration of E.
coli and enterococci in wastewater.
Improve workflow and keep testing costs down.For total coliforms
and E. coli, the IDEXX Colilert® family of tests can be run two ways.
If run as a presence/absence test, Colilert is an easy, accurate way
to comply with the TCR. For quantitative testing, IDEXX offers the Quanti-Tray® and Quanti-Tray®/2000 methods. When run in conjunction
with Colilert, they provide counts up to 2,419 per 100 mL without the
need for filtration or dilutions. Quanti-Tray and Quanti-Tray/2000 can
also be run in conjunction with Enterolert®,
a quantitative test for enterococci. A variety of regulatory publications include IDEXX methods
(see chart below).
- Colilert and Colilert®-18
are included with Quanti-Tray
in the Ambient Water Rule, the LT2 Rule and the proposed Wastewater
Rule for the detection of E. coli.
- Enterolert, in
conjunction with Quanti-Tray, is included for the enumeration of
enterococci in the Ambient Water Rule and the proposed Wastewater
Rule.
- Filta-Max®, the IDEXX Cryptosporidium
and Giardia capture and concentration method, is validated
as part of U.S. EPA Method 1623. Method 1623 is specified in the LT2
Rule for the capture and detection of Cryptosporidium.
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TECH TIP
The large overflow well in Quanti-Tray and
Quanti-Tray/2000 is a valid test well and should be counted if
positive in the determination of MPN/100 mL.
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| Regulation |
Analysis |
IDEXX Methods Included |
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| Ambient Water Rule |
E. coli and enterococci |
Colilert, Colilert-18, Enterolert and
Quanti-Tray |
| Groundwater Rule (proposed) |
E. coli and enterococci |
Colilert, Colilert-18, Colisure, Enterolert and Quanti-Tray |
| LT2 Rule (proposed) |
E. coli and Cryptosporidium |
Colilert, Colilert-18, Quanti-Tray and
Filta-Max® |
| Total Coliform Rule |
Total coliforms and E. coli |
Colilert, Colilert-18, Colisure and Quanti-Tray |
| Surface Water Treatment Rule |
Total coliforms and HPC |
Colilert and
SimPlate® for HPC |
| Wastewater Rule (proposed) |
E. coli and enterococci |
Colilert, Colilert-18, Enterolert and
Quanti-Tray |
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