Environmental Project No. 1155 – Coliform bacteria and E. coli in drinking water. Comparison of EU reference method with alternative methods

Coliform bacteria and E. coli in drinking water. Comparison of EU reference method with alternative methods

5 Final conclusion

In this final conclusion the data from the Danish equivalency studies with spiked as well as natural drinking water samples are summarized.

The overall conclusion is that the Danish EPA approved Colilert as an alternative method to the EU reference method (EN ISO 9308-1:2000) for the examination of drinking water for coliform bacteria and E. coli.

Colilert was shown to be equivalent to the EU reference method for the detection of coliform bacteria and E. coli in spiked samples with a low background flora. Furthermore the same study with spiked samples confirmed well-known problems by using the reference method for detection of coliform bacteria and E. coli in waters with high heterotrophic counts due to overgrowth of the membrane filters. Colilert showed good recoveries in the same samples.

The study demonstrated that the problem with overgrown filters was seen also for three other membrane filtration methods: LSA37, Chromogenic agar and Chromocult.

MLGA showed relatively good recoveries in spiked samples, but the method was excluded from the further studies due to technical reasons.

The Danish reference method until now (DS 2255:2001) was included in testing of natural drinking water samples where it was found not to be able to detect coliform bacteria in any of 15 samples where one or more of three other methods (EU Reference method, Colilert and Chromogenic agar) detected coliform bacteria.