She is the first woman and the first Singaporean to win the award, which is into its 11th year.
She was picked from among the 49 country finalists vying for the title, each of whom had already been named the Ernst & Young Entrepreneur Of The Year in their home countries.
Ms Lum said she is thankful to the many "angels" who supported and guided her, including her board members and staff.
She also said she hoped her win will inspire more women to participate in the annual competition.
Ms Lum founded Hyflux in 1989 with two employees and a start-up capital of S$20,000. She has been the driving force behind the company's growth and business expansion.
The company has since become a public-listed group with a market capitalisation of about S$1.8 billion, employing more than 2,000 people worldwide.
Hyflux is also a leading membrane-based, desalination supplier, and is currently building the world's largest seawater reverse osmosis desalination plant in Algeria.
It also has operations and projects in South-east Asia, China, India, the Middle East and North Africa.