The first ever Olympic water polo tournament was held in Paris in 1900, in the river Seine. Yes, they played water polo smack in the middle of the river. Sounds pretty cool, actually. Belgium finished second.
1904 was skipped, but water polo returned in 1908, when Great Britain somehow got a bye all the way to the final. Belgium had to play two games to get there. They finished second.
In 1912, Belgium finished third. The war canceled 1916, but in 1920, led by Jewish brothers Gerard and Maurice Blitz, Belgium finished... second.
In 1924, the brothers returned, and Belgium promptly finished... second.
In 1928, Maurice was off the team, but Gerard competed. The dang Germans knocked out the Belgians before they had a chance for a medal. Belgium skipped 1932, but Gerard had a final chance at glory in 1936, when they finished... (you guessed wrong!) third.
So, two silvers for Maurice, and two silvers and a bronze for Gerard, plus a bronze in swimming in 1920.
Belgium never medalled in water polo again.