After military service at a hot air balloon base, he joined his father and his brother Étienne in the industrial water purification business in Le Cateau.
He successfully installed an iron filtration system for the water supply in Saigon-Cholon (now Ho Chi Minh City) in Vietnam in 1933.
[2] His father Émile retired in 1939, and the company was split between Gilbert and Étienne, who ran the mechanical construction workshop in Le Cateau.
World War II slowed business in Le Cateau, as Allied bombings destroyed the canal system used to transport goods such as steel, vital to the construction of water filters.
[3] Degrémont formed close working relationships with three men, with whom he would grow the business over the subsequent decades: Pierre Duflot, who ran the financial part of the business, Sarkis Balabanian, who focused on foreign expansion, and Roger Leviel, chief engineer and specialist in chemistry and water.
He was notorious for his inability to speak English (a characteristic which many managers loyally follow today), but he spoke Spanish well enough to win business first in Spain and later in South America, notably in Cali, Colombia, and Lima, Peru, in the 1950s.