The students see that the engineers are a tight team, working well together.
Their visit is part of a class on Singapore's hidden communities. Later, in the classroom, they admit that until then, few had given a thought to the highly skilled professionals who look after Singapore's water supply.
The awareness of the "soft" ramifications of hard-nosed business decisions is an aspect of a topic raised by Prime Minister Lee Hsien Loong last month - that of local universities having a wider national and social mission beyond grades and rankings.
He urged them to imbue "Singaporean values and ethos, the spirit of wanting to contribute back to society and the sense that they have a responsibility to take Singapore forward".
Says NUS' vice-provost for student life, Professor Tan Tai Yong: "The university in the 1970s and the 1980s was essentially to produce the right manpower to drive the economy.
"As society becomes more advanced, it's not just about fitting people into certain sectors of the economy, but for them to play leadership roles."
Insight looks at this education shift, and how it's happening.
What needs to change
Singapore's schooling system has resulted in a disproportionate focus on grades and academic achievements, say university leaders, who seek to address this by emphasising more holistic education.
For many students, exposure to community service comes via the compulsory Community Involvement Programme (CIP).
It may not be the ideal way to foster a social conscience; some recall that activities teachers chose for them - picking up litter in parks, visiting an old folks' home - were a brief "touch-and-go" experience that did little to change them.
No surprise then that when students step onto campus, they are preoccupied with getting their degrees.
Nanyang Technological University (NTU) provost Freddy Boey says: "They have been so primed to just push for academic studies. So in the first year, we need to give them a rounded picture - that life in university is not exam after exam."
NTU does this with freshmen at orientation, encouraging them to take part in student groups and other activities.
The importance of developing a more rounded, socially aware individual comes as national leaders worry about social cohesion amid widening income gaps.
The Government aims for 40 per cent of each final-year school cohort to go on to university by 2020. Many will become bosses, managers, doctors,lawyers, decision-makers and leaders. They cannot afford to lack understanding about, and empathy for, other members of society.
And while parents continue to have a key role in imparting values, universities believe they can also influence youth who are more mature and yet open to exploring new ideas.
The carrot, or the stick?
Singapore's six universities each have their own views about how best to stir the student conscience.
Some, like the Singapore Management University (SMU), mandate community service to ensure every student gets involved.
SIM University (UniSIM) and the Singapore Institute of Technology (SIT) will also make such participation compulsory when they start offering their own full-time degrees next year.
On the other hand, Singapore's other three national universities - NUS, NTU and the Singapore University of Technology and Design (SUTD) - believe that students will resent compulsion or do community service just to get the credits, without real passion for it.
They prefer to encourage them through education, and providing space and funding for student projects and club activities.
NTU's Prof Boey says: "Community service is from the heart, not from the head. The worst thing you can do is to require them to go for community service before they graduate. That sends all the wrong signals and we will not change their behaviour."
However, SMU president Arnoud De Meyer cites figures to the contrary: Although students must do at least 80 hours of community service or roughly two weeks in their four years of education, on average, they give 120 hours - and some, 400 hours - suggesting that a desire to do more emerges voluntarily.
Getting students' buy-in could lie in the way community service is mandated.
Unlike the teacher-directed CIP, SMU students get to choose their own projects with help from a Centre for Social Responsibility, set up in 2011. Six staff members guide students on best practices in community engagement and social entrepreneurship.
SMU student Nelson Goh says he and his peers initially resented the 80-hour requirement.
But now the fourth-year business undergraduate thinks compulsion is not a bad thing: "Most people in my generation don't put ourselves out there. If not for it, I would not have gone out of my comfort zone.
"The turning point was when I realised I should make the best use of it, and surrounded myself with like-minded individuals and started to think of ideas that impact the most people."
So he and 15 others went to Kenya in 2011, refurbishing and teaching at an orphanage, and he has returned every year.
SMU's Dr De Meyer says it is looking into recognising students for the leadership they show not only in clubs but also in big community service projects by giving them credits that count towards their degree. But they would need to write a report and reflect on what they have learnt.
NTU's Prof Boey differs, likening such practices to how parents do grassroots work so that their children have a better chance of getting into a primary school.
University leaders in this camp are looking for a culture change, starting with those students who are willing, and enabling them to pursue their passion.
NTU cut curriculum time by 20 per cent to encourage its 23,500 undergraduates to pursue their passion, including community service, on top of work attachments.
This reduction is possible, Prof Boey gives the assurance, because students are smarter these days and technology allows them to learn faster. NTU will also move to more online learning.
It will also build two new student learning hubs costing $100 million over the next three years for student activities, including community work here and abroad. Funding for such work could come from donors' endowments, he adds.
Prof Boey is hopeful of a culture change, perhaps in three or four years: "All we need are some early stories of students who pioneer voluntary work, play the story up, encourage other students. People's mindset can change."
SUTD, too, gives students autonomy and time to pursue their passion, with no classes on Wednesday and Friday afternoons, but makes a bigger push to integrate this with class learning.
Second-year undergrad Amos Chia, 23, this year took part in a project to improve sanitation in a community in the Philippines. But what took this to a different level was a compulsory course in world civilisations. He says that this enabled him, as a student in engineering product development, to better see issues from different perspectives.
So in the Philippines, by making sure the programme did not interfere with the community's Sunday mass and daily life, the people were more willing to work with the students.
Now, in class, he is using his increased social awareness in a group project to design a wheelchair that can be merged with a bed to help elderly patients.
On how this awareness helps in the design process, he explains: "Depending on their facial expressions, you can understand if they are uncomfortable. These kinds of reactions are more accurate to spot discomfort."
SUTD president Thomas Magnanti, former dean of Massachusetts Institute of Technology's school of engineering, says: "You get more innovation by enabling than by legislating. You let people release their passion."
Unlike long-established NUS and NTU, SUTD is only two years old and so has been able to tap new trends and hire faculty not just strong in academics and research, but who subscribe to its social mission. With 130 faculty members and just over 600 students, there is also more interaction.
NUS' Prof Tan says some departments do integrate learning with social change, but by and large, each discipline will say it needs the curriculum time to train students.
Instead, it is expanding its residential college programmes to engage students more deeply on issues such as social change.
Unlike university halls of residence, these colleges have experiential learning courses, like the one on hidden communities, and where there is much learning in small groups.
It aims to have over two-thirds of its freshmen take part in residential college programmes, up from 35 per cent now.
At one residential college at NUS, the College of Alice and Peter Tan, students have initiated a project on health education for the elderly in Tanglin Halt and another project to encourage youth in a neighbourhood school.
The students spent time singing karaoke with the old folk to build rapport and understand first their main health concern - fractures. Others played basketball with the young and realised they needed motivation, not tuition.
As for freshman Tan Kuan Liang, 20, who visited the PUB engineers, he used to think that being socially conscious meant getting hands-on in the community. Now he knows being aware of others who are different in society is important.
His teacher, Dr Tan Lai Yong, who trained as a medical doctor and is known for his 14 years of service in Yunnan working on community development among poor villages, says he does not use words like "giving back to society", but that he and others are simply training students to be aware that there are people who are different, "nothing so altruistic as to turn them into social heroes".
He notes: "To be an effective professional, you need two things: competence and communication. To communicate well, you need to listen well, you need to be able to hold diverse views and you don't do that very well from afar." Such awareness can only benefit the likes of future potential decision-makers such as Mr Tan Kuan Liang, who is on a
Singapore Armed Forces scholarship and will serve as a regular officer in the infantry - imbued with a sense, as PM Lee put it, that they have a responsibility to "take Singapore forward".