BACTERIOLOGICAL ANALYSIS OF DRINKING WATER
INTERPRETATION OF THE RESULTS, DISINFECTION & PREVENTIVE ADVISES
Microbiological water analysis done by proven methods is the only safe way to judge the drinkability of the
water.
INTERPRETATION OF RESULTS & DESIRABLE RESULTS
Fecal coliforms and Enterococcus count:
The presence of fecal coliforms (Escherichia coli) and Enterococcus count in the water show the evidence of
human or animal contamination and the possible presence of enteric pathogens. Any water that contains these
bacteria must not be consumed.
Acceptable quantity: < 1 CFU/100 mL
Results not in standards: 7 1 CFU/100 mL Non drinkable water, during all the period of contamination, it is
important to boil the water for at least 5 minutes before its consumption. Proceed to the desinfection of the well.
Total coliform count:
The presence of total coliforms in the water does not generally indicate the contamination from fecal matter or
sanitary risks but from the degradation of the bacterial quality of the water. This degradation can be attributed to
the infiltration of surface water in the well. Most of these species can be found naturally in the ground and in the
vegetation. The analysis of total coliforms allows to obtain information on the possible vulnerability of a well
from the pollution present on the surface. As soon as their number exceeds 10 CFU / 100 mL, we suggest that
you proceed to a preventive desinfection.
Acceptable quantity: = 10 CFU/100 mL
Results not in standards: > 10 CFU/100 mL. Proceed to the desinfection of the well.
Atypical colonies:
The research for total coliforms also allows to detect the presence of atypical colonies (colonies that do not
possess the expected colonial morphology (appearance and color) in the employed cultured environment. If these
bacteria are found in great amount (>200 CFU/100 mL), they can mask the presence of total coliforms. The
water that comes from a protected well generally possesses a low level of bacterial population.
Acceptable quantity: = 200 CFU/100 mL
Results not in standards: > 200 CFU/100 mL. Proceed to the desinfection of the well.
Preventive advises:
It is recommended to do the analysis of drinking water (provided from wells, lakes, rivers, etc) at least once or
twice a year, at the beginning of spring and in the fall (abundance of water). An analysis is recommended if the
well was not maintained and/or has not been used for a long period of time, due to major reparation or the
installation of a new well. It is recommended to disinfect the well before proceeding to analysis. If your results
exceed the acceptable quantity, you have to search for the source of contamination and resolve the problem.
Disinfecting the well with bleach can restore the situation. After desinfection, you will have to do a
bacteriological analysis again to insure that you obtained the needed water quality. If the problem persists after
all these procedures, the desinfection and the bacteriological analysis have to be done once again. If the problem
is still present after the second desinfection, then it is recommended to install a permanent treating system.
Form 81-19 R1 (E)
2009-06-30
Exova
121 Hymus Boulevard • Pointe-Claire • Quebec • H9R 1E6 • Telephone: +1 514 697-3273 • Fax: +1 514 697-2090
Page 1 of 2
The references on the certificate of analysis:
These terms mean the methodological reference used during the principal water analysis. They are expressed in
codes for internal laboratory purposes.
The results and the units:
The results represent the quantity of bacteria found in the analyzed water portion. They are expressed in Colony
Forming Unit (CFU) per 100 mL. The sign ‘<’ means ‘Less than’, the sign ‘>’ means ‘More than’ and the sign
‘=’ means ‘Less than or equal to’.
DESINFECTION PROCEDURE OF A WELL
If possible, please take off all strange bodies, animal or vegetable matters with the use of a scoop (bailer);
•
Pour in the well the required quantity of bleach (see table below) (50 mg/L free chlorine insure an effective
desinfection;
•
Open all the faucets; when the odor of chlorine becomes perceptible, stop the pomp and close all the faucets;
•
Keep everything rest for 24 hours;
•
Open again all the faucets until the odor of chlorine disappears;
•
One week later after the desinfection, a water sample should be taken to make a bacteriological analysis;
•
We also suggest you to make an extra verification after 4 weeks.
Artesian Well
Diameter
[ millimeters/ inches]
50 / 2
65 / 21/2
76 / 3
89 / 31/2
102 / 4
127 / 5
152 / 6
Surface of the well
Diameter
[ meters/ feet ]
1.0 / 3
1.5 / 5
2.0 / 61/2
2.5 / 8
3.0 / 10
3.5 / 111/2
4.0 / 13
0.914 / 3
1.067 / 31/2
1.219 / 4
1.372 / 41/2
1.524 / 5
1.676 / 51/2
0.7 L
0.9 L
1.2 L
1.5 L
1.8 L
2.2 L
1.0 L
1.4 L
1.8 L
2.2 L
2.7 L
3.3 L
1.3 L
1.8 L
2.3 L
3.0 L
3.7 L
4.4 L
1.6 L
2.2 L
2.9 L
3.7 L
4.6 L
5.5 L
2.0 L
2.7 L
3.5 L
4.4 L
5.5 L
6.6 L
2.3 L
3.1 L
4.0 L
5.2 L
6.4 L
7.7 L
2.6 L
3.6 L
4.7 L
5.9 L
7.3 L
8.8 L
Depth of the well [ meters / feet – approximation ]
15 / 50
30 / 100
45 / 150
60 / 200
30 mL
50 mL
60 mL
90 mL
120 mL
190 mL
270 mL
60 mL
100 mL
140 mL
190 mL
250 mL
380 mL
540 mL
90 mL
150 mL
200 mL
280 mL
370 mL
570 mL
820 mL
120 mL
190 mL
270 mL
400 mL
500 mL
800 mL
1100 mL
Water depth [ meters / feet – approximation ]
REFERENCE: The quantities in his table are taken from Environmental Minister of Quebec, « Le Puits », 2003 (Envirodoq ENV/2003/0256)
Form 81-19 R1 (E)
2009-06-30
Exova
121 Hymus Boulevard • Pointe-Claire • Quebec • H9R 1E6 • Telephone: +1 514 697-3273 • Fax: +1 514 697-2090
Page 2 of 2