Application of Standards for Bacteriological Quality of Public Drinking Water Supplies

1. If the required continuous disinfection is not being provided, an immediate boil water advisory is recommended.
2. Bacteriological samples shall be taken at representative locations in the distribution system and must include the beginning and the end of the system, in accordance with the recommended number of samples. Disinfection residuals must be checked and recorded for each sampling point. For potable water dispensing units (PWDUs), disinfection residuals need not be checked.
3. If no disinfectant residual is detected at the sampling location, the operator of the system shall be advised of the fact that no residual is detected, and in consultation with the appropriate authorities and in accordance with existing guidelines, remedial action shall be initiated. This may include the issuing of a boil water advisory for the area affected by the lack of disinfectant residual.
4. If the bacteriological test reveals the presence of E.coli, re-sampling of the site, as well as up and downstream locations, should be carried out within 24 hours. However, a boil water advisory may be recommended before the re-sampling results are known depending upon the extent of E.coli contamination in the initial testing, combined with knowledge of other problems pertaining to the water system. Regardless, if the repeat test reveals the presence of E.coli, a boil water advisory is recommended.
5. If the bacteriological test reveals the presence of total coliforms, but no E.coli, re-sampling of the site, as well as up and downstream locations, should be carried out as soon as is practically possible. If the consecutive test confirms the presence of total coliforms, but no E.coli, a boil water advisory is recommended for water systems that have only disinfection but no additional water treatment (such as coagulation, sedimentation, filtration or equivalent technologies) or have no significant operational procedures and controls over the water system. Regardless, remedial action shall commence in consultation with the water system operator.
6. If repeat samples cannot be taken as per paragraphs 4 and 5, a boil advisory is recommended.
7. Reporting of results pertaining to these standards shall be done in accordance with the provincial “Guidelines for the Issuance of Boil Water Advisories“.

Rescinding of Boil Water Advisories:

Boil advisories may be rescinded upon correction of the condition(s) which led to the boil advisory. At least two consecutive samples must meet the bacteriological and disinfection standards. All officials must be advised.

Rev: July 2, 2008

Application of Standards for Bacteriological Quality of Private Wells

Please refer to the following webpage for information on how bacteriological quality standards for private wells (unsatisfactory, substandard, and satisfactory results) are applied:  Water Testing Interpretation | Newfoundland & Labrador Public Health Laboratory