The producer - who served as a judge on Popstars: The Rivals when the group was formed - praised them for the achievement.
"It's amazing how they've been worked. Brilliant," Waterman told the Daily Star.
"From a show that everyone tells me was a piece of garbage, we had number one, number one and number three in the Christmas charts and one of the acts is still around ten years later."
He went on to joke: "But we didn't know what we were doing."
Photo gallery - Girls Aloud's career in pictures:
Copyright: Rex Features ITV/Rex Features
Girls Aloud recently celebrated their tenth anniversary by releasing retrospective collection Ten, which featured new singles 'Something New' and 'Beautiful Cause You Love Me'.
Meanwhile, the rescheduled Pete Waterman Presents The Hit Factory concert will take place at London's O2 Arena on December 21.
The show will include performances from Steps, Jason Donovan, Rick Astley, Kylie Minogue and Sinitta.
Watch the music video for Girls Aloud's 'Something New' below: