takes from two to six days, in a sophisticated laboratory, to obtain a total coliform count.
Their tests cannot determine specific indication of whether fecal contamination has
occurred. Test invalidation may be caused by growth and interference from non-
coliform heterotrophic bacteria. However, the Colilert method overcomes these
problems and confirmed results take 24 hours or less. With Colilert, coliforms
metabolize specific indicator nutrients, liberating a yellow color for the presence of total
coliforms and a fluorescence color for the presence of E. coli. A negative test sample is
indicated by no yellow color within 24 hours.
A national study conducted by the American Water Works Association
Research Foundation (AWWARF) and the United States Environmental
Protection Agency (USEPA) in 1987 documented that no confirmation test is
required when Colilert is used. The Washington office of EPA has approved
Colilert as an alternate standard method for total coliform analysis.
(a) Wash hands thoroughly and work surface prior to performing the
(b) Remove one unit dosed tube from the box.
(c) Remove one sterile reaction vessel from its wrapper. Label the cap
to reflect the date, time, and sample identification.
The inside of the water collecting vessel/bag, Colilert cap or tube, and the
water sample must remain sterile. Keep objects and fingers from these
Mix the water sample vigorously and thoroughly.
(e) Uncap one sterile vessel. Leave the cap inverted on the clean
Never open a Colilert tube until it is ready to be used to prevent possible
Pour 100 ml of the water sample into the reaction vessel.
(g) Add the contents of one unit dosed tube of Colilert reagent to the
reaction vessel. Replace the cap of the vessel, without touching its interior surface.
Then tighten the cap and mix vigorously to dissolve the reagent.
It is normal if some reagent particles remain undissolved.