Water FAQ 2

Guidelines for Canadian Drinking Water Quality
You will need to understand two technical terms to be able to interpret the results:
• Maximum Acceptable Concentration (MAC) is a level that has been established for certain substances that are known or suspected to cause adverse health effects.
• Aesthetic Objective (AO) is established for parameters that may impair the taste, smell, or colour of water or which may interfere with the supply of good quality water.

Detection Limit
The detection limit is the lowest concentration of a chemical that can be reliably measured. It may be referred to on a lab report as DL, RDL (reporting detection limit), or RL (reporting limit).

The detection limit depends on the equipment used for analysis and the method of analysis. It can also be affected by the concentration of other parameters present in the water. For example, if the concentration of calcium is very high, it can elevate the detection limit of another parameter. To compare the concentration of a parameter to the Canadian drinking water quality guideline (if one exists), the detection limit must be less than the guideline.

Some labs do not report the detection limit. However, you can still determine the detection limit used for each parameter from the lab report. For example, if the detection limit of a parameter is 2 mg/L and the level of the parameter is below the detection limit, the result will be listed as “< 2” (less than 2 mg/L).

If the detection limit is greater than the guideline, you should consult the laboratory where the analysis was done. The laboratory will inform you of the options available for reporting the parameter of concern with a lower detection limit.

Units
Laboratories may report the concentration of parameters in milligrams per litre (mg/L) or micrograms per litre (μg/L or ug/L).

There is a BIG difference: 1 mg/L is equal to 1000 μg/L.
When looking at the results from a lab and comparing them to previous results, or to the results from a different lab, or to the Guidelines for Canadian Drinking Water Quality, make sure the units are the same.

1 mg/L = 1000 micrograms per liter (μg/L)
1 mg/L = 1 part per million (ppm)
1μg/L = 1 part per billion (ppb)