South Africa competed in the Empire Games from 1930 until 1958, after which it left the Commonwealth. South Africa rejoined the Commonwealth after 1994, and it's atheletes competed in the Commonwealth Games since then.
Listed below are the South African medal winners at each Empire and Commonwealth Games - those who have not also won world titles or Olympic medals.

Springbok team to the 1930 Empire Games, held in Hamilton, Ontario.

Molly competed at the 1934 and 1938 Commonwealth Games, winning a silver medal in the relays at both events.

In 1938 Hazel - on the left, with Molly Ryde and Carla Gerke -  won a silver medal in the 330 Yard Medley Relayat the Commonwealth Games held in Sydney.

Jacobus Coenradus de Beer "Jackie" Wiid  was a backstroke swimmer who won a gold medal in the 100m event at the 1950 Commonwealth Games in Auckland. In the 100m freestyle he finished 5th. He also competed at the 1948 Olympic Games held in London, where he finished 6th. 

Felicity was a swimmer from the University of Pretoria who won a gold medal at the 1954 Commonwealth Games. She was a member of the 4x110 yard freestyle relay team with Joan Harrison, Maggie Petzer and Natalie Myburgh.

Peter (on the right, with Les Klenerman) was 2nd in the 1954 Commonwealth Games 1650 yards Freestyle, 3rd in the 1954 Commonwealth Games 4x220 yards Freestyle Relay. He was one of 4 South African swimmers, and the diver Ernie de Jong, who accepted scholarships to the university of Oklahoma in late 1952. 

'Billy' Steuart finished 3rd in the 1954 Commonwealth Games 4x220 yards Freestyle Relay, with Dennis Ford, Graham Johnston, and Peter Duncan. In 1958 and 1959 NCAA Championships he won and defended his titles for both 440 yards and 1650 yards freestyle.

Like Joan Harrison, Dennis Ford came from East London, but attended King Edward (KES) in Johanneburg, where he swam  with coach Cecil Colwin.  At the 1954 British Empire and Commonwealth Games he took home a bronze medal in the 4x220 yard relay.

Murray "Tich" McLachlan (seconds from the left) was a Natal swimmer who won 4 titles at the 1960 South African swimming championships. He had won a bronze medal in the 1650 yards freestyle event at the 1958 Commonwealth Games in Cardiff, and swam the 1500m at the 1960 Rome Olympic Games, where he finished a creditable 6th. 

At the 1958 Commonwealth Games in Cardiff, Peter won a silver medal in the 220 yards breaststroke . 

Two-times an Olympian in 1996 and 2000, Helene won silver medals for the 100m freestyle and 4x100m freestyle relay at the 2002 Manchester Commonwealth Games. Helene on the righrt with Charlene Wittstock, Sarah Poewe and Mandy Loots.  At the NCAA Championships in 2000 Helene won a bronze medal in the 200 mteres freestyle.

Mandy attended the Eden Glen High School in Edenvale, and swam with coach Dean Price at the Dolfins club in Johannesburg. In 2002 Mandy won a silver medal in the 100m butterfly at the Commonwealth Games in Manchester.

Paul Roos Gymnasium 2014, Commonwealth Games medallist, Olympian and Rhodes Scholar. At the 2010 Commonwealth Games in India he won the silver medal in the 1500 meter freestyle and as a member of the 4X200 meter freestyle relay team, they took the bronze.

Gideon Abraham Louw won three medals at the 2010 Commonwealth Games in Delhi. He swam at the Olympic Games in 2008 and 2012, and in 2009 he won two relay titles at the NCAA Championships with Auburn University.

Like Jan Venter, Jean won a bronze medal in the 4x200m freestyle relay at the 2010 Commonwealth Games in Delhi. At the 2008 Olympic Games in Beijing Jean finished 4th in the 200m freestyle, 0,8 seconds behind the bronze medal winner.

Riaan won bronze in the 40 IM at the 2010 Commonwealth Games in Delhi. He competes in freestyle and medley events, and was the 2009 Midmar Mile winner. Schoeman represented South Africa at the 2008 Olympics in Beijing and the 2012 Olympics in London. His brother Henri Schoeman won bronze in the triathlon at the 2012 Olympic Games. 

Sebastien represented South Africa in the 2010 and 2014 Commonwealth Games, in Delhi and Glasgow respectively. At the 2014 Commonwealth Games, he won bronze medals in the 400m individual medley, 200m butterfly, 4 × 200 m freestyle relay and 4 × 100 m medley relay. He also swam at three Olympic Games

Calvyn is backstroke specialist who in 2018  placed third in the 4x100 medley relay at the Commonwealth Games, along with team mates Chad Le Clos, Cameron van der Burgh and Brad Tandy. He swam in the 4x200 freeestle relay at the 2016 Olympic Games.