Nice to see someone find and recycle underwater housing for obsolete analog video camcorders for extremely underrated Super 8 film. Unfortunately, the film looks like it has some flaws in it it should not have and I've shot Tri-X before. As for the water leak, you're lucky your Canon Zoom 318 was not wiped out, as that has happened to many a camera in underwater situations that the filmmaker thought was safe (test these things in a bathtub submerged, people). It also looks like the plastic the Canon lens films through might be a bit fogged or a hair or bit of dust might be in the Canon lens?
There are several underwater Super 8 film housings that exist including one Bauer did for their Mini camera, which was also a silent 18 frames-per-second only like the Canon 318. The Ewa-Marine company made a few dozen different underwater cases that covered a few hundred Super 8 models before switching to video cameras. These are now hard to find and need special treatment before use.
Some underwater housings for 16mm film cameras even exist that might work with Super 8, but others might be too small to find another camera for like the the Marine for Fuji's tiny AX100 camera for their own Super 8 format called Single 8, their version of Super 8 with a totally different cartridge despite the same-sized film.
The real crown jewel of underwater Super 8 shooting is the Eumig Nautica, which did not need any underwater housing and could be submerged as is! They are very costly now starting at about $250.00 and much higher, but they are great and even have accessories like lenses and a special Surf Set. It too only does silent 18 frames-per-second filming, but the company (under new ownership) does conversions to a sound 24 frames-per-second rate at a high price. Some have been able to do the upgrade themselves.
As for film to shoot on your next surf trips, you might find older Kodak Plus-X or even 4-X for a different black and white look or really old GAF 500 ASA black and white if you can find it. ADOX has a 100 ASA panchromatic black & white film try out, a Foma 100 ASA black & white cartridge was also issued, Kahl in Germany (on line) has unique color and black & white, Kodak has great Vision 3 color negative film to try to go with the return of Ektachrome 100D and companies like Spectra, Wittner and Pro8mm offer as many kinds if film stocks as possible in Super 8.
Super 8 never died, is as alive as ever, is coming back to life in a new wave of rediscovery and let's hope we see more filmmaking like this more often.