This is the first time scientists have measured and compared profiles of the substance in detail across multiple alien worlds.
According to researchers, finding of water in the atmospheres of these planets marks a step forward in the search for distant planets that may be capable of supporting alien life.
The strengths of their water signatures varied, it said.
WASP-17b, a planet with an especially puffed-up atmosphere, and HD209458b had the strongest signals.
