Water Testing – What to do?

What Should I Do If I Have an Unsatisfactory or Substandard Test Result?


  1. Verify the safe condition/construction of the well including the wellhead, pump, plumbing, well liner and surrounding area. Correct any problems that are identified. Where the fecal coliform E. coli is detected in a water sample, sources of fecal contaminations such as improperly working septic systems, wild animals, domestic animals and pets should also be considered.
  2. Shock chlorinate the well and plumbing system (see instructions in the tables below), then flush the system to remove chlorine and retest the water no sooner than 48 hours after shock chlorination.
  3. If the water remains contaminated after the shock chlorination, continue to boil the drinking water and consider the following:
    • an appropriate disinfection device
    • well reconstruction
    • well replacement


How Can Well Water Be Disinfected?

If test results are unsatisfactory of substandard, it is necessary to shock treat the well and, if possible, find and eliminate the source of contamination. Disinfection can be done using unscented household bleach. The following tables outline the quantitiy of bleach required to properly disinfect new and existing wells.


Volume of bleach to be added to New Wells*


Depth of Water in Well Casing Diameter
15 cm (drilled) 90 cm (dug)
1.0 m 100 mL 3.2 L
3.0 m 300 mL 9.8 L
5.0 m 500 mL 16.5 L
10.0 m 1000 mL 32.0 L


* New wells require a high chlorine concentration


Volume of bleach to be added to Existing Wells


Depth of Water in Well Casing Diameter
15 cm (drilled) 90 cm (dug)
1.0 m 20 mL 0.6 L
3.0 m 60 mL 2.0 L
5.0 m 100 mL 3.0 L
10.0 m 200 mL 6.5 L



Steps for Chlorine Disinfection

  • Add the amount of unscented bleach determined according to the table above to the bottom of the well and then agitate the water. Connect a garden hose to a nearby tap and wash down the inside of the well. This will ensure thorough mixing of the chlorine and the water throughout the well.
  • Open each tap and allow the water to run through all taps until a smell of chlorine is detected, then turn off the taps. If a strong smell is not detected, add more bleach to the well.
  • Allow the water to sit in the system for 12-24 hours.
  • Run water through the outside hose away from grass and shrubbery until the strong smell of chlorine disappears. Make certain that the water does not enter any watercourse. Finally, open the indoor taps until the system is completely flushed.
  • Wait a minimum of 48 hours, then take a sample of the water for bacteriological testing. Satisfactory results in repeat tests over a period of one to three weeks following chlorination will probably indicate that the treatment has been effective. In the meantime, find another source of water or boil the water for one minute before drinking it. Do not use untreated water such as roadside springs.
  • If the shock treatment solves the problem, repeat bacteriological testing in three to four months.
  • If the above steps do not alleviate the problem, it is recommended that the source of the ongoing contamination be determined and corrected, possibly with professional help. If remediation is not possible, a permanent alternative solution, such as a new well or a drinking water disinfection device, should be considered.


How Can Small Volumes of Contaminated Water Be Made Bacteriologically Safe For Drinking?



Bring water to a vigorous boil for one minute and allow to cool; this is by far the most reliable method.



To treat small amounts of water use unscented household bleach at the rate of at least two drops per each litre of water and allow the water to stand for 30 minutes. If the water is turbid or cloudy, double the number of drops.



For More Information

If you have any questions about drinking water safety, please contact the Service NL location nearest you or visit this website.


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