installation having a population of 2,000 would require 10 samples per month. Assume
the following test results from the test samples (membrane-filter technique):
Filtration
Colonies
Volume
per
Sample No.
ml
No. Colonies
100 ml
Acceptable
1
100
0
0
Yes
2
100
0
0
Yes
3
100
5
5
No
4
100
0
0
Yes
5
100
2
0
Yes
6
100
0
0
Yes
7
100
2
2
No
8
100
0
0
Yes
9
100
0
0
Yes
10
100
0
0
Yes
Total 7
Monthly average = 7 = 0.7 colonies/100 ml
10
(3) The test results show the water supply meets the criterion of an average
monthly coliform density of less than 1 per ml and not more than one sample exceeding
4 colonies per 100 ml (where the total number of samples per month is less than 20).
However, since sample number three, above, shows more than four colonies per 100
ml, daily samples must be taken from collection point number three until the results of at
least two consecutive samples show less than one coliform per 100 ml.
3-14. STANDARDS FOR GARRISON WATER SUPPLIES
a Samples. The number and frequency of samples for bacteriological analysis
of garrison potable water supplies will be determined by the appropriate federal
regulation, local facility engineer, and responsible preventive medicine personnel. The
number of troops served, the situation, and local determining factors would be taken
into account.
b. Multiple--tube Technique. In water testing, the multiple-tube technique has
standard samples. Each sample must comprise of five standard portions of 10 ml each).
Therefore,:
(a) Coliforms shall not be present in more than 10 percent of the
portions per month, or;
(b) Nor more than 1 sample may have 3 or more portions positive
when less than 20 samples are collected per month, or;
MD0160
3-27