Background Comparing injury death rates by region is a commonly used method to identify regions with higher risk. To correct for exposure, other denominator other than population has been used, such as per miles driven for motor vehicle injuries or per hours flown for injuries in aircraft. We sought to compare regional drowning death rates using population as denominator versus that using area of natural water as denominator.

Methods Drowning deaths in 16 regions in Taitung County Taiwan by for years 2008 through 2013 were collected as numerator in calculating drowning death rates. Mid-year population in 16 regions were used as the first denominator in calculating drowning death rates. Area of natural water (lakes, rivers, streams, beach etc.) in 16 regions were obtained from Water Resource Agency, Ministry of Economic Affair, Taiwan were used as the second denominator in calculating drowning death rates.

Results The rankings of drowning death rates by region according two denominators differed greatly. The drowning death rate using population as denominator in Taitung City was 6.0 per 100,000 population, which ranked 10^th among 16 regions in Taitung County. The drowning death rate using area of natural water as denominator in Taitung City was 355 per square km, which ranked the 1st among 16 regions in Taitung County. We further collected data from fire bureau of Taitung County Government and found a clustering of 8 drowning deaths from 2010 through 2014 in one lake in Taitung City.

Conclusions To identify regions with higher risk of dying from drowning, we recommend of calculating drowning death rate using area of natural water as denominator as a supplement in addition to traditional drowning death rate using population as denominator.