A water bacterial test is a simple screening test for checking drinking water and well water for total coliform bacteria. The test uses a 100 ml water sample and provides an easy-to-read colour result after 48 hours at room temperature.
When should drinking water be tested?
- Private well water should be tested regularly, generally every three to five years.
- Test the water if its colour, taste or odour changes.
- Testing is also recommended after flooding, heavy rainfall or other events that may allow surface water to enter the well.
- Water may contain bacteria even when it looks, smells and tastes normal.
How to use the water bacterial test
The bottle is sterile and airtight. It contains a dry culture medium with meat extract, peptone, lactose, pancreatic digest of casein, proteose peptone no. 3, dipotassium phosphate, monopotassium phosphate, sodium chloride, sodium lauryl sulphate and bromocresol purple.
- Open the sterile bottle immediately before testing.
- Add 100 ml of the water sample to the bottle.
- Close the cap tightly and shake until the dry culture medium has dissolved.
- Keep the closed bottle at room temperature for 48 hours.
- Read the result by checking the colour of the liquid.
How to interpret the result
Purple or unchanged colour: the test has not detected total coliform bacteria in the sample.
Yellow-orange or yellow: the result indicates suspected bacterial contamination. Do not use the water for drinking or food preparation until its safety has been assessed. Contact your local environmental health authority or an accredited water laboratory for further testing and advice.
What does the test not tell you?
This water bacterial test screens for total coliform bacteria. It does not measure all microorganisms or chemical contaminants such as nitrate, nitrite, metals, pesticides, pH or water hardness. A negative result therefore does not by itself prove that the water meets every drinking-water quality requirement. Laboratory analysis is recommended whenever comprehensive information or an official assessment is needed.
Frequently asked questions
What does a water bacterial test detect?
It screens a water sample for total coliform bacteria. These bacteria may indicate that surface water or other contamination has entered the water source.
How long does the test take?
The result is read after the sealed test bottle has remained at room temperature for 48 hours.
What should I do if the result is positive?
A yellow-orange or yellow result should be confirmed through an accredited water laboratory. Ask your local environmental health authority for instructions and avoid using the water for drinking or cooking until it has been assessed.
Can this test confirm that well water is safe to drink?
No. A single home test cannot assess every aspect of drinking-water quality. This test provides information about total coliform bacteria only.
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