TNI Logo The NELAC Institute

Standard Interpretation

SIR #: 98
Standard: 2009 TNI
Section: V1M5, Section (c)


The lab conducts SM9020a testing on potable water only. We purchase single use sterile water from IDEXX who also manufactures the Colilert media. It is their recommendation to use sterile water in blanks and dilutions. This is the only use our lab has for sterile water as everything else is prepackaged ready to use. The sterile water comes in sealed 100ml aliquots with reagent water criteria certification from IDEXX. The water is purchased in lots and the lot is verified upon receipt for pH, conductance and sterility. It is stored in a refrigerator at 4C. The lab is small and only conducts 20 tests per month. Is the in house QA and manufacture certification of the sterile water sufficient for the use of the water as a lot per TNI standards - or should it be conform to predisposed buffer water standards?


(Microbiology Expert Committee and NELAP AC, 9-23-15)

Under the current standard, the requirement is to check the purchased water once per lot and, in addition, once per month when using a bottle that lasts longer than one month. If the water is to be used for preparation of media, reagents or as a diluent, which will put it in contact with microorganisms, then the requirements of verification as stated in EL-V1M5-2009 are needed along with the verification of sterility.