Winger Hawkridge, 23, and central defender Waterfall, 22, have both signed one-year deals with the club and follow new Scunthorpe chairman Peter Swann to Glanford Park from Gainsborough.
Former Gainsborough chairman Swann replaced predecessor Steve Wharton last month.
Hawkridge told the club's official website: "It's a massive step. It's obviously two leagues from Gainsborough and before then I jumped two leagues from Carlton to Gainsborough so yes, I'm looking forward to it."
Former Barnsley and Tranmere defender Waterfall added: "Obviously it's going to be a challenge, it's two leagues above, but I'm hoping I can prove myself to the manager and the fans and hopefully get in there and do well.
"I've been in the Football League when I was younger so I know what goes off so I prepared for the games at Gainsborough as I will do here - do it professionally, that's the way I am."
- Sports & Recreation