The study found that antibiotic concentrations in some waterways were 300 times higher than safe levels.
The researchers found that Ghana, Bangladesh, Kenya, Nigeria and Pakistan were home to the most contaminated rivers.
The researchers, who examined 14 antibiotics commonly used in rivers across 72 countries, found that safety limits were most often exceeded in Asia and Africa.
However, sites in Europe, North America and South America also had high levels of contamination, indicating that antibiotic contamination was a “global problem”.
Scientists are concerned that antibiotics in rivers will cause bacteria resistance, which means they can no longer be used in medicines for humans. The UN estimates that increasing antibiotic resistance could kill 10 million people by 2050.
“A lot of the resistance genes we see in human pathogens come from environmental bacteria,” said Guardian William Gaze, a microbial ecologist at Exeter University who was not involved in the study.