Water pressure is invisible until a tap is too weak—or too strong.
Singapore’s drinking-water network has to serve landed homes close to sea level, HDB blocks, hospitals, commercial towers and buildings whose highest fittings sit far above the pressure that ordinary public mains can supply directly.
The solution is not one islandwide pressure setting.
PUB uses service reservoirs and public mains to create the city-scale pressure network. Buildings then add tanks and pumps where elevation requires them. Tall buildings can be divided into pressure zones so lower floors are not exposed to excessive pressure merely because upper floors need more head.
The public operating chain is: treated water → service reservoir → public main → building meter → direct supply where pressure is sufficient, or transfer tank → pumps → high-level/intermediate tanks → gravity or controlled pump supply → individual fittings.
1. Pressure comes from elevation and pumps
Water stored at a higher elevation possesses gravitational head.
As it flows downward through pipes, that elevation difference becomes pressure.
Where natural elevation is insufficient, pumps add energy to move water upward or maintain pressure during periods of high demand.
2. Service reservoirs create a city-scale pressure buffer
PUB operates more than ten service reservoirs, including facilities for potable water and NEWater.
Traditional service reservoirs are placed on high ground so gravity can help maintain stable and consistent pressure through the public network.
They also buffer the difference between steady treatment-plant production and demand that rises and falls through the day.
3. Peak demand is a hydraulic timing problem
Water demand is not constant.
Morning showers, cooking, schools and commercial activity can raise demand quickly. Later periods may be much quieter.
Storage allows the network to accumulate water during lower-demand periods and release more during peaks without requiring treatment plants to change output instantly every time thousands of taps open together.
4. PUB mains can serve lower fittings directly
PUB’s current water-supply handbook linked from its professional guides specifies direct supply from public mains where the highest fitting does not exceed 25 metres above mean sea level.
In this range, the building can rely on the public network pressure rather than storing and repumping all water internally.
Direct supply is simpler because it removes some tanks, pumps and maintenance interfaces.
5. Above 25 metres, high-level storage begins to matter
For highest fittings above 25 metres but within the handbook’s stated range up to 37 metres, PUB specifies indirect supply through a high-level water storage tank.
The tank changes the hydraulic arrangement.
Instead of expecting every upper-floor fitting to receive enough pressure directly from the street main, the building stores water at elevation and distributes it internally.
6. Above 37 metres, a transfer tank and pumps are required by the handbook arrangement
For premises whose highest fittings are beyond the reach of direct mains pressure, PUB’s handbook specifies a low-level water transfer tank with pumping to a high-level storage tank.
The public main fills the low-level tank through the metered connection. Pumps then lift water to the high-level tank.
The building has effectively inserted its own vertical distribution stage between the city main and the upper floors.
7. High-level tanks turn pump energy back into gravity
Pumps do the work of lifting water upward.
Once the water is stored at height, gravity can supply many floors below without every tap requiring its own active pump.
The high-level tank therefore acts like a small private service reservoir inside the building.
8. One rooftop tank can create too much pressure at lower floors
A very tall column of water creates high pressure at its base.
If a skyscraper supplied every lower floor directly from one very high tank, some lower-level fittings could experience pressure much higher than desirable.
That is why tall buildings divide water service into pressure zones.
9. Intermediate tanks divide the vertical column
PUB’s water-efficiency guidance describes intermediate tanks as one way to reduce excessive pressure in tall buildings.
An intermediate tank can serve a designated group of floors and can also act as a transfer stage toward a higher tank.
The building therefore becomes several smaller hydraulic systems stacked vertically instead of one enormous pressure column.
10. Pressure-reducing devices can perform a similar zoning job
Depending on the building design, pressure-reducing valves and other control devices can limit pressure delivered to lower zones.
The objective is the same: upper floors need enough pressure while lower floors should not receive unnecessarily high pressure that stresses fittings, increases leakage or wastes water.
11. Bidadari shows that service reservoirs do not always have to sit on hills
The Bidadari Underground Service Reservoir is Singapore’s first service reservoir built on low ground within a new estate.
Instead of relying primarily on natural elevation, it combines underground storage with centrally operated pumps to boost network pressure during peak water-usage periods.
During lower-demand periods, the reservoir is replenished with potable water from other high-ground service reservoirs.
12. Bidadari uses up to five pumps to support the estate
PUB states that Bidadari’s facility can supply homes through up to five centrally operated pumps during peak usage.
The pumps allow a low-ground reservoir to perform a pressure-support role traditionally associated with high-ground storage.
The design trades some pumping energy for land efficiency and local network resilience.
13. Underground storage saves surface land
Bidadari’s two underground tanks hold potable water while the land above is integrated with park space.
PUB states that the surface footprint is about one-third that of a typical service reservoir of similar capacity, saving roughly 1,500 square metres of land.
The facility therefore solves pressure, storage and land-use problems together.
14. Building tanks create a water-quality responsibility inside private premises
Once drinking water enters a building storage tank, the building owner or MCST becomes responsible for maintaining part of the drinking-water chain.
A poorly maintained tank can become a source of contamination even though the water entering it from PUB was safe.
The public network and private building system therefore meet at a quality handoff as well as a pressure handoff.
15. Water storage tanks require annual inspection and certification
PUB’s current water-storage-tank guidance requires the responsible building owner or MCST to engage a Licensed Plumber at least once every 12 months to inspect the tank and, where necessary, clean and disinfect it before certification.
PUB also conducts random inspections.
Storage therefore creates maintenance obligations that direct mains supply does not impose on the same scale.
16. Pumps need redundancy because water demand does not stop when one motor fails
Where a building depends on pumps to reach upper floors, pump failure becomes a water-supply risk.
Professional water-service design therefore uses appropriate duty and standby arrangements, controls and storage so one component fault does not immediately leave an entire tower dry.
The precise configuration belongs to the building’s Professional Engineer and Licensed Plumber under the applicable PUB and SS 636 requirements.
17. Water-service design with pumps or tanks requires professional responsibility
PUB’s plumbing guidance states that where water-service works involve a pumping system or storage tank, a Professional Engineer must be engaged for design and supervision.
Licensed Plumbers also carry regulated responsibilities for installation and certification.
This reflects the consequence of getting the hydraulic design wrong: low pressure, excessive pressure, contamination risk or system failure can affect many occupants at once.
18. A worked example: 40-storey residential tower
Imagine a tall residential tower whose upper fittings are far beyond the elevation at which direct public-main pressure is adequate.
The public main supplies a low-level transfer tank. Pumps lift water to higher storage. The building is divided into pressure zones so lower floors do not receive the full head of the highest tank. Intermediate tanks or pressure-control devices serve selected levels. Each storage tank remains subject to maintenance and certification requirements.
The resident opens one tap. The building has quietly performed several hydraulic transformations before water appears.
19. Common misconceptions
Misconception: PUB mains directly pressurise every tap in every skyscraper.
No. tall buildings use tanks, pumps and internal pressure zones when elevation exceeds direct-supply capability.
Misconception: More pressure is always better.
No. excessive pressure stresses fittings, can increase leakage and needs to be controlled on lower floors.
Misconception: A rooftop tank only stores emergency water.
No. in many high-rise systems it is part of ordinary hydraulic distribution.
Misconception: Water quality is entirely PUB’s responsibility once water enters the building.
No. building owners and MCSTs have legal maintenance duties for private storage tanks and water-service installations.
20. The deeper idea: a vertical city turns height into infrastructure
Horizontal distance costs pipe friction. Vertical distance costs pressure.
Singapore’s water network solves the island scale with treatment plants, reservoirs and mains. Tall buildings then inherit a second problem that did not exist at street level: how to lift water high enough without crushing the floors below under excessive pressure.
Tanks, pumps and pressure zones convert one tower into several manageable hydraulic layers.
The skyline works because each building quietly builds a small water network inside the larger one.