William Slater had the following podium finishes at major championships: 3rd in the 1958 British Empire and Commonwealth Games 4×220 yards Freestyle Relay (with Kenneth Williams, Cam Grout, and the non-Olympian Peter Bell). Slater also finished fourth in the 1650 yards freestyle and was eliminated in the heats of the 440 yards at the 1958 British Empire and Commonwealth Games.
|1956 Summer||16||Melbourne||Swimming||Men's 400 metres Freestyle||Canada||CAN||3 h4 r1/2|
|1956 Summer||16||Melbourne||Swimming||Men's 1,500 metres Freestyle||Canada||CAN||5|
|1956 Summer||16||Melbourne||Swimming||Canada||Round One||Heat Four||3||4:40.4|
|1956 Summer||16||Melbourne||Swimming||Canada||Round One||Heat One||3||QU||18:51.6|