However, he had a long-lived passion for water polo: this led him to later become one of the rare world sportsmen to compete at the highest level in two different team sports.

Rubini chose water polo, and he won a gold medal in the sport, at the 1948 Summer Olympic Games, in London, beating the Hungary in the final.

With Rubini as a full-time player, Italy could boast what was to be called the "Golden Settebello", one of the most valuable water polo teams ever, which also won a bronze medal at the 1952 Summer Olympics, and at the Turin European Championship of 1954.

Later, as the delegation head of the senior Italian national basketball team, Rubini also took part in the first international victories of Italy: these include the silver medal at the 1980 Summer Olympic Games.

Rubini was involved with his beloved sports until his death: he promoted water polo formation for young athletes, and was the Honorary President of Olimpia Milano.