A study by the Centre for Addictions Research at the University of Victoria said that's a problem because surveys of alcohol consumption are crucial to estimating disease and injury caused by people's favourite recreational drug.
The centre's director, Tim Stockwell, said it's easier for society to ignore the risks associated with alcohol consumption when policies are based on a gross underestimation of how much people actually drink.
The study, published in the journal Addiction, found that Canadians under age 24 are most likely to under-report how much alcohol they drink, and there's no difference in the amounts of lowballing by men and women.
Data included in the study are from the first three years of daily Health Canada phone surveys of 45,000 people across the country between 2008 and 2012.
Canadians were asked what type of alcohol and how many drinks they'd had over the last week, the last month, the last year and the day before — a question that provided the most accurate information based on memory, said Stockwell, who is also a psychology professor at UVic.
He said the results showed people reported only about one third of their consumption when the amounts were compared to how much alcohol was actually sold every year — 8.2 litres of pure alcohol per person aged 15 and over.
That amounts to 480 bottles of beer, 91 bottles of wine or 27 bottles of spirits, Stockwell said.
Canadians in the North are likely to drink an average of 13 litres or more and residents in Eastern Canada drink the least compared to national figures — possibly because of the price of alcohol, he said.
The study suggested respondents who reported drinking once a month, on average, were likely to have consumed alcohol twice a month. Someone who said they drank once a week actually partook twice, and respondents who said they imbibed every day in a week consumed alcohol six times.
National low-risk guidelines in Canada recommend women have no more than two drinks a day, or 10 a week, and that men consume no more than three a day, or 15 drinks a week.
Stockwell said wine drinkers were more likely to under-report their consumption, possibly because unlike beer in a bottle or can, the size of a drink of wine is not fixed.
"People have their wine topped up so it's very hard to keep track of it."
Unlike in other countries, including the United Kingdom, Australia, and New Zealand, labels on bottles of alcohol in Canada, and the United States, don't include the number of standard drinks, making it hard to gauge how much guzzling is going on.
"So Canadians generally have a very poor, misty idea of how much they drink," Stockwell said.
The study results could lead to better policies regarding alcohol, which he said causes about 10 times more harm compared to illicit drugs.
Gerald Thomas, an alcohol researcher associated with the Canadian Centre on Substance Abuse in Ottawa, said the study results show that while there is often a focus on alcoholics, there should also be more of a recognition about people who overdrink, often leading to health risks and violence.
He said the data suggest that Canada, as one of the few countries in the world with government-owned liquor stores, should maintain such monopolies to control the availability of alcohol.