Williams, a 19-year-old hooker who began the season playing in the club’s Under-20s, has become a first-team regular this season.
Scorpions director Marc Lovering is pleased to have added two players of such pedigree to the club’s plans for next season.
“Christiaan is a leader on the pitch,” he said.
“He is not necessarily the most vocal but he leads by example. You are guaranteed 100% effort and commitment from Roetsy and that rubs off on the players around him.
“He’s a proven international centre and great to have around the place.
“We could and perhaps should have had a few more points on the board than we have but I think anybody that has watched us this season knows we are moving in the right direction and making progress.
“For a player of Christiaan’s calibre to commit to us again says a lot about where we are as a club and what we are looking to achieve.
“The World Cup is fast approaching and I do not think Roetsy would have committed had he thought we would still be languishing around the bottom of the table next year. Our coach Phil Carleton has to take a great deal of credit for that.
“Both re-signings are really important to us albeit probably for differing reasons.
“Any promising 16 to 18 year olds in South Wales just need to look at the progress Zak has made in the past few seasons.
“He probably got thrown into the first team a little too early and perhaps in the wrong way last season but Mike Grady, the head coach at the time, had very few options.
“The introduction of the under 20 side has allowed players like Zak to play some games against their contemporaries and gain more confidence.”