Lum started corporate life as a chemist with Glaxo Pharmaceutical. After working for three years at Glaxo, she left in 1989 at the age of 28 to start up Hydrochem, the precursor to Hyflux, with just SG$20,000 of capital, which she raised by selling her condominium and car.She hired three employees at the start; Lum herself rode around on a motorcycle selling her company's water filters and treatment chemicals. By January 2001, Hyflux had become the first water treatment company to be listed on SESDAQ, and was upgraded to the Singapore Exchange's Mainboard in April 2003.