Water quality — The variability of test results and the uncertainty of measurement of microbiological enumeration methods

This International Standard gives guidelines for the evaluation of uncertainty in quantitative microbiological

analyses based on enumeration of microbial particles by culture. It covers all variants of colony count methods

and most probable number estimates.

Two approaches, the component (also known as bottom up or step by step) and a modified global (top down)

approach are included.

The aim is to specify how values of intralaboratory operational variability and combined uncertainty for final

test results can be obtained.

The procedures are not applicable to methods other than enumeration methods.

NOTE 1 Most annexes are normative. However, only the annexes relevant to each case are to be applied. If the choice

is the global approach, then all normative annexes that belong to the component approach can be skipped and vice versa.

NOTE 2 Pre-analytical sampling variance at the source is outside the scope of this International Standard, but needs

to be addressed in sampling designs and monitoring programmes.

NOTE 3 The doubt or uncertainty of decisions based on the use of analytical results whose uncertainty has been

estimated is outside the scope of this International St