Abstract

A third trial with reference materials for water microbiology was organized. Thirty-eight Dutch laboratories and 39 laboratories of the EC participated. The design of the trial was the same as in the first and the second trial. Also the test strains were the same: WR1 Escherichia coli and WR3 Enterobacter cloacae. The reference materials of the third trial were more stble and homogeneous than the batches used in the first and the second trial. Improved materials and protocols resulted in better performance in participating laboratories. The variation between the results was less than in the first and the second trial. Insufficient inhibition of the growth of test strain WR3 at a nominal temperature of 44 C, in some laboratories, showed that incubation at 44 C still need some improvements. The use of reference materials may therefore be very useful.