Figure 3-2. Water testing kit, bacteriological.
b. Sterilization of Equipment.
Funnel and filter-support assembly.
(a) The funnel and filter-support assembly should be sterile at the
beginning of each filtration series. It is not necessary to sterilize this assembly between
successive filtrations or between successive filtrations of a series of samples unless an
interruption of 30 or more minutes occurs between them. The probability of
contaminating each succeeding sample with bacteria present in the previous one is
reduced by properly flushing the funnel walls with sterile buffered water.
(b) The preferred method for sterilizing the funnel and filter-support
assembly is in an autoclave. The funnel and filter holder should be wrapped separately
in kraft paper and sterilized in the autoclave at 121C (249.8F) for 15 minutes. At the
end of the 15-minute holding period, the steam pressure should be released rapidly to
(c) The funnel and filter holder may be sterilized in a flowing steam
sterilizer for a 30-minute holding period.
(d) In an emergency, or in the field when an autoclave or sterilizer is
not available, the funnel and filter holder may be sterilized by keeping it immersed in
boiling water for 10 minutes.