The advice comes after a coronial investigation concluded last week that the death last year of Ulverstone bushwalker Jonathan Paul Dent, 30, was most likely caused by hyponatraemia, or overhydration.

University of Tasmania health science lecturer Greig Watson has researched and compiled hydration studies for 20 years.

He said overhydration, while rare, tended to occur in people exercising or exerting themselves physically for more than four hours.

Dr Watson said the overdrinking diluted blood- sodium levels which can lead to central nervous dysfunction, possibly a coma, even death.

"For someone who weighs 70 kilos, if they consume a litre an hour more than they sweat, there is the possibility that they are going to dilute their blood-sodium levels," he said.

"For smaller people, if you consume about 700ml of water in an hour than you actually need, per hour, in four hours."

Severe symptoms of the condition include brain-swelling, swollen wrists and ankles, vomiting, increased body mass, confusion, and seizures.

Dr Watson said people who tended to get fluid-overloaded were slower athletes with a lower sweat rate who had time to drink. He said hyponatraemia can occur in marathons and triathlons.

KFM Fitness Studio personal trainer Callan Richardson said water should be used to replace and replenish what had been lost in exercise.

"You can do it by scales but the best thing to do is to listen to your body," he said.

"Sport drinks are good when you are feeling particularly dehydrated but should only be used in moderation because of the amount of sugar they contain."

Bushwalking Tasmania president David Atkins said bushwalkers were made aware of the risks of hyponatraemia (overhydration) through first aid training courses.

"It has never been a major concern any more than the concern of a snake bite in the bush," he said.

He said sports drinks tended to maintain sodium levels slightly better than plain water slightly.