NAN HUA High student Lek Yan Ru realises that the world cannot take the environment for granted after watching a documentary in class.

The 14-year-old Secondary 2 student said: 'Now, I wash a full load of laundry each time instead of half a load. I re-use water from washing rice to water plants.'

Her school is one of four secondary schools that have introduced environmental education modules in their curriculum to enhance students' knowledge of green issues.

Since last year, Secondary 1 students at Marsiling Secondary have been taking a 30-hour module on water management. The programme was extended to Secondary 2 students this year, with a module on air quality and ways to prevent air pollution.

Nan Hua High, as well as Commonwealth Secondary and Nanyang Girls' High introduced similar courses this year.

Madam Koh Saw Eng, the Department Head for Science at Marsiling Secondary, said it was important to understand environmental issues - like climate change and the depletion of natural resources.

She said: 'We give the students tasks so that they learn through self-discovery.'

Dr Amy Khor, Senior Parliamentary Secretary, Ministry for the Environment and Water Resources, praised the schools for their efforts, at the opening of the Clean and Green (CGS) Singapore Schools' Carnival on Tuesday at the Suntec Exhibition Hall.

She said the National Environment Agency (NEA) is looking into working with these schools to develop environmental education modules for other schools.

The CGS Schools Carnival showcases joint environmental projects with corporate partners under the NEA Corporate and School Partnership Programme.

Princess Elizabeth Primary School and Fujitsu Microelectronics Asia received the third prize this year for developing an eco-friendly aquarium.

It has a filtration system which uses bacteria to clean up waste, and the water in the aquarium needs to be changed only once every two years instead of once in two months, saving 4,550 litres of water over two years.