Oversized plumbing adds millions to Australian building costs, thanks to standard dating back to 1940s

Outdated plumbing standards lead to oversized systems and inflated costs for Australian apartment buildings. Their plumbing systems are required to handle a water demand that is more than three times the actual recorded peak demand, our recently published research shows.

The “designed peak demand” as stated in the Australian plumbing standard dictates the design and scale of water services in apartment buildings. The large gap between predicted demand and actual demand in most of these buildings means that the water system is much larger than necessary, increasing construction and maintenance costs.

A case study of a 13-storey apartment building, it is estimated that A$120,000 could have been saved in construction costs if actual peak demand had been used for the plumbing design. With hundreds of buildings built in Australia every year, the updated standards could save millions of dollars.

An even bigger problem is that oversized systems don’t work as expected. This leads to plumbing faults which represent a high proportion strata insurance claims and cost the Australian economy about $200 million per year.



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We can improve plumbing systems by using more accurate peak demand estimates. However, it is not just about reducing the size of pipes and pumps. This can create other damaging problems such as noisy vibrations in the pipes called water hammer.

Updating the standard requires work to develop a modern and accurate process for sizing plumbing systems.

Plumbing standards and practices are outdated

The Australian plumbing standard provides a solution for sizing water services to plumbing code of australia. Based on the number of apartments, the solution estimates the likely maximum water demand – the “designed peak demand”. The pipe size is then determined based on a desired range for the rate at which the water flows and the water pressure at times of peak use.

Hunter’s work (1940) laid the foundations of plumbing engineering.

This approach is based on theBarrie Book”. It was developed using the UK plumbing code in the mid 1970s. UK plumbing codes and many other international codes are based on artwork by Roy B. Hunter in the United States, which was published in 1940.

Hunter monitored the use of water taps in two hotel buildings during times of high demand. He used the data to determine the likelihood of using each type of device at those times. Knowing the throughput of the device and the number of devices, the likely total demand can be determined.

We are much more water efficient today

The overstatement of buildings today is not a reflection of Hunter’s work. This is the result of changes in our use of water and advances in plumbing technology.

In Australia, the Water efficiency labeling and standards adopted in response to the millennium drought have largely resulted in changes in fixture flows and water use. For example, consumption in our two largest cities has fallen by a quarter to a third this century.

In Melbourne, residents used an average of 248 liters per person per day (L/p/d) in 2001. In 2020, it was 158 L/p/d.

Line graph of Melbourne's water consumption history per capita

Residential and total daily water use per person in Melbourne from 2001 to 2020, and projected use.
Draft Urban Water and System Strategy for Greater Melbourne: Water for Life/Melbourne Water, Author provided

In Sydney, demand fell by around 270 L/p/d to 200 L/p/d during the same period.

Line graph showing total daily demand and residential drinking water use per person in Sydney from 1991 to 2021

Total daily demand and residential use of drinking water per person in Sydney from 1991 to 2021.
Water Conservation Report 2020-2021/Sydney Water, Author provided

Oversized systems are expensive

A case study of a 13-storey residential building with approximately 120 apartments found that the pipe size would have been 40 mm instead of 100 mm if it had been designed for the actual peak demand. This could save $120,000 in construction costs. This suggests that very large savings could be made in the construction sector.

For the hot water system, the smaller pipe could reduce heat loss by 30-40%, saving an additional $2,000 per year in energy costs.

Oversized pumps due to an overestimation of peak demand are less energy efficient and cost more. They start and stop more often, to “reduce” the water flow, which reduces the life of the pump. Water hammer can also create water hammer.



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Building water pipes with cracks at the joint.
Image: James Gong

To deliver a given amount of water, wider pipes have lower flow velocities than narrower pipes, so oversized pipes can rarely experience self-cleaning velocities. These relatively high flow rates remove trapped air and particles that can cause pipe walls wear out faster. Long-term low flows also promote growth of biofilms and bacteriawhich can lead corrosion and discolored water.

Repeated water hammer, combined with other factors such as water chemistrycan lead to plumbing systems fail prematurely. When this occurs after the expiration of a property developer’s defaults and liability period (usually in two years for non-structural defects), the owners remain responsible for a hidden design problem.

A 2021 condominium insurance report listed ‘water damage including leaks’ and ‘burst water pipe’ among the four most common causes of complaints in Australia. The combined claims costs were estimated at more than 500 million dollars from 2016 to 2020, based on a review of approximately 49% of all strata schemes in Australia. This equates to an annual national cost of $200 million.


Graphic: The conversation. Data: N. Johnston, A Data-Based Holistic Understanding of Strata Insurance in Australia and New Zealand/Strata Community Association, CC PER


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How can we improve plumbing design?

Deakin researchers are developing methods to more accurately estimate peak demand for multi-level residential buildings. Digital water meters have provided a rich data set that shows how Australians use water indoors.

With more accurate peak demand estimates, pipe sizes would be reduced significantly using the existing standardized approach. However, smaller pipes may experience more severe water hammer and a higher risk of pipe erosion and corrosion due to higher throughput.

Future plumbing design must consider a wide range of flow conditions. Most of the time the throughput is well below the expected peak demand, but it can change quickly. Modeling can help us understand how systems perform under various conditions.

Capturing the dynamics of flow, pressure, temperature and power consumption is a challenge that requires further research. Australian plumbing standards and practices require systematic updating that goes beyond peak demand.