(a) Municipal (treated) supplies: 100, 200, or 300 ml. Preference
should be given to these volumes in the order in which they are listed.
(b) Untreated supplies: 50 or 100 ml.
(c) Water from mains before resumption of service repairs or from new
mains: 100 ml.
(2) Raw water sources.
(a) Unpolluted surface water: 5 to 50 ml.
(b) Polluted surface water: 0.01 to 10 ml.
FILTRATION AND INCUBATION
The following practices and procedures are desirable for effective application of
the membrane filter technique:
a. Clean the work area with water; then allow the surface to dry.
b. Prepare fresh medium for the day's testing. If ampules are used, one ampule
is required for each sample filtration.
c. Arrange and prepare certain equipment and supplies from the bacteriological
water testing kit (see figure 3-2) for use as follows:
(1) Open the bottle of methanol and place forceps in it so that the tips are
immersed approximately 1 inch.
(2) Position the Bunsen or alcohol burner. It will be used to " burn the
alcohol off the tips of the forceps before they are used.
(3) Label the petri dishes with the sample number shown on DO Form 686,
the date and time, analysist's initials, and the volume filtered. Position them on the work
(4) Place one sterile absorbent pad in each petri dish. Use sterile forceps to
manipulate it. Before using the forceps, be sure to burn the alcohol off their tips. Do not
hold the forceps in the flame any longer than necessary to ignite the alcohol since
excessive heat will damage the forceps.
(5) Use a sterile pipette to deliver enough laboratory prepared culture
medium to saturate each absorbent pad or empty the contents of one ampule of
medium on each absorbent pad (see figure 3-3). The amount of culture medium
required for each absorbent pad is approximately 2 milliliters. The amount should be
sufficient to allow a large drop to drain from the pad freely when the petri dish is tipped.