People with epilepsy are up to 19 times more likely to drown than those in the general population, research suggests.
A University College London review of 51 studies from around the world showed 88 deaths where five would be expected, adding many could have been prevented.
Taking showers instead of baths and swimming with a friend could save lives in the event of a seizure, suggests the report in Neurology journal.
Epilepsy affects around one in every 131 people in the UK.
People with the condition are more at risk of accidental death and a higher chance of drowning had been reported, but the risk had never been quantified.
A team at the Institute of Neurology at University College London looked at data from 51 studies from around the world.
They compared the number of deaths from drowning with what would be expected in the general population of the country involved.
Overall the risk was 19 times higher for people with epilepsy and in England and Wales specifically the increased risk was 15 times higher.
Study leader Professor Ley Sander, who works part-time as an NHS consultant in epilepsy, said he had two patients die from drowning this year alone.
"The numbers are relatively small but the important thing is that these deaths are preventable.
"Every year a number of patients die in the bath so convincing people to take showers would be life-saving."
He added: "We're not saying that people shouldn't swim but that they need to be aware of the risk and to go with someone who can help if they have problems."
Professor Sander also advised telling a lifeguard if swimming at a swimming pool and to swim during quieter sessions so it was easier for the lifeguard to see them.
He stressed that those most at risk were the people with "active" epilepsy and who had regular seizures.
"We always need to do whatever we can to ensure seizure control," he said.
A spokesperson for Epilepsy Action said: "People with epilepsy can enjoy the benefits of taking part in many water activities, but need to take sensible precautions to reduce risk of drowning.
"Because there is always a possibility that a seizure could happen, it is important not to underestimate the potential risks when in or near water."