Around 600 teenagers set off on Wednesday for a three-day tour of the mainland, during which they will learn about how fresh water from a mountain range 300 kilometres north of Hong Kong is supplied to the city through an intricate network of pipelines and tunnels first built 60 years ago.

The trip, sponsored by a youth foundation, takes students to an artificial lake in Guangdong, as well as Sanbai mountain in Jiangxi, situated in a national forest park known for its pristine water quality.

Addressing the students at West Kowloon station before they boarded a chartered high-speed train to Heyuan, Secretary for Home and Youth Affairs Alice Mak urged the youngsters to spare a thought for the city’s residents who endured a severe drought in the 1960s.

The drought led to a landmark agreement that saw the mainland supply Hong Kong with fresh water from Dongjiang, a tributary of Pearl River.

Some of the students on the trip hail from ethnic minority backgrounds.

They included Zarina Insar, a 14-year-old from Pakistan who said she wanted to learn more about the water supply system.

Zayan Khan, who’s 15, said he signed up for the tour after spotting a promotional poster.

"I'm very happy. I haven’t been to Dongjiang [region], but I actually learnt a little about the history [of Dongjiang water] and now I want to see how the water is supplied to Hong Kong," he said in Cantonese.

Insar, Khan and 38 others on the trip are attending Islamic Kasim Tuet Memorial College in Chai Wan.

School principal Zareenah Ho said some of them also come from Egypt, Malaysia and Palestine.

"Most of them have never been to the mainland," she said.

"A few visited in the past year or two, thanks to policies from the government.

"We also like to thank the organiser for arranging halal meals and prayer facilities for our Islam students."

Ho hoped the trip can enrich students' understanding of the nation’s development and help them learn to appreciate the water they consume every day.