The International Centre for Diarrhoeal Disease Research, Bangladesh has been treating up to 650 patients a day since the weekend, according to consultant physician Mark Pietroni.
"What we are seeing now is probably related to the flood waters receding," he told AFP.
He said the Dhaka hospital normally treated mainly children under the age of five, and was currently seeing a high numbers of adult patients who were severely dehydrated.
The hospital usually sees about 400 new patients a day at this time of year, he said.
"It's about a 50 percent increase on the background figures we have for this time of year."
The hospital had erected tents with a capacity of 750 patients in the parking areas adjacent to the hospital, and increased staff numbers.
About 1.5 million people were affected by flooding in several parts of Bangladesh last week.
The country's Flood Forecasting and Warning Centre anticipates flooding to be completely gone by the weekend.
Bangladesh is criss-crossed by a network of 230 rivers, most of them tributaries of the Ganges and Brahmaputra.
The low-lying country suffers annual floods, with at least a fifth of the country submerged each year.