It began with more focused efforts to spread the word about the importance of conserving water through orientation activities and videos back in 2014.

The message has since seeped in for inmates in facilities under the Singapore Prison Service (SPS), who would actively point out water leaks.

The SPS also introduced a system to monitor daily water usage and installed presto taps or thimbles in water taps to reduce the water flow in its prisons.

These efforts contributed to it using 12.8 per cent less water last year than in 2013, helping it to become one of the four winners of this year's Watermark Awards.

This annual award, which is in its 10th year, recognises individuals and organisations for their contributions to the conservation of Singapore's water resources.

The other three winners, chosen from a pool of 35 by national water agency PUB, are Tampines North Primary School, Pratt & Whitney, and the Nee Soon South Clean and Green Committee.

The prize ceremony will take place tomorrow at Marina Barrage.

Deputy Commissioner of Prisons and SPS chief of staff Shie Yong Lee said of the award: "It's an affirmation of not just the efforts of our staff, but also our inmates and our partners."

Another of this year's winners, aero-engine firm Pratt & Whitney, decreased its water usage by 8 per cent, or more than 10.2 million litres of water, last year.

One thing it did to achieve this was to install vacuum distillation units to recycle waste water in four of its facilities here.

Using a baseline year of 2006, the firm - which employs more than 2,000 people in Singapore - aims to reduce its water consumption by 80 per cent by 2025.

Executive director Kevin Kirkpatrick said: "We've been on this journey of sustainability for a long time and it's nice to get recognition.

"When it comes to sustainability, it goes across all our processes, whether it's electricity, water, waste - it's something that is ingrained in the culture."