Canadian Nuclear Safety Commission (CNSC) document Standards and Guidelines for Tritium in Drinking Water, explains these differences in more detail. Canada has chosen to use a reference dose level of 0.1 mSv/year for limiting tritium. This is 10% of the general radiation dose limit for the public. It is 20-30 times lower than the total amount of radiation that an individual would receive in a year from all sources of natural background radiation.
Recently, the Ontario government considered lowering the tritium limits in that Province. In response to this proposal, the CRPA wrote a position paper demonstrating that there was in fact no need to reduce the limits. There were several reasons for this, including the fact that there was no scientific basis for the proposed decrease.
As you can see from this information page on the CNSC website, there may be some areas where tritium concentrations in groundwater are higher than others, but this is due to historical activities, and the locations are well known. It is illegal to discharge any tritium directly to groundwater. Any groundwater which does have elevated levels of tritium is not used as a source of drinking water and does not pose a health risk to the public.