5.1 Microbiological water testing procedures using membrane filtration are based on the premise that all bacteria within a specific size range will be retained by the membrane filter used. If the membrane filter does not retain these bacteria, false negative results or lowered density estimates may occur that could have serious repercussions due to the presence of unrecognized potential health hazards in the water being tested, especially in drinking water.

5.1.1 This procedure as devised will enable the user to test each membrane filter lot number for its ability to retain all bacterial equal to, or larger than, the stated membrane pore size.

5.2 Since this membrane is often used to sterilize nonautoclavable liquids, it is essential that the retention characteristics of this membrane are stable.

1.1 This test method covers a procedure to test membrane filters for their ability to retain bacteria whose diameter is equal to or slightly larger than the 0.2-µm pore size of the membrane filter.

1.2 The procedures described are for the use of user laboratories as differentiated from manufacturers' laboratories.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.