Where did Thailand host the inaugural games that included swimming, diving and water polo events?
Aquatics at the 1975 Southeast Asian Games: Aquatics at the 1975 Southeast Asian Peninsular Games included swimming, diving and water polo events. 1975 Southeast Asian Peninsular Games:  South Vietnam, Cambodia and Laos, which only sent token squads made up of military personnel to previous games, declined to participate due to internal political problems.
South Vietnam, Cambodia