Two teams of scientists used NASA's Hubble telescope to look at the rate of absorption of light through these planets' atmospheres. They looked out for infrared wavelengths associated with water signatures as this light was absorbed.
Researchers compared the absorption patterns for these planets and are confident they have found water on multiple planets.
"We're very confident that we see a water signature for multiple planets," said Avi Mandell, a planetary scientist at NASA, and lead author of the paper describing three of the five planets, WASP-12b, WASP-17b and WASP-19b.
"This work really opens the door for comparing how much water is present in atmospheres on different kinds of exoplanets, for example hotter versus cooler ones," Mandell said.
The water signals from the five planets were fainter than scientists expected and they feel that can be attributed to haze or dust blankets around these planets.
"To actually detect the atmosphere of an exoplanet is extraordinarily difficult. But we were able to pull out a very clear signal, and it is water," said Drake Deming of the University of Maryland, whose team described HD209458b and XO-1b in the second study.
The five planets are hot Jupiters, massive worlds that orbit close to their host stars. The researchers were initially surprised that all five appeared to be hazy, but Deming and Mandell noted that other researchers are finding evidence of haze around exoplanets.
"This suggests that cloudy or hazy atmospheres may in fact be rather common for hot Jupiters," said Heather Knutson, a co-author on Deming's study.