The most common plumbing system design in the developed world is based on the hydraulic performance of gravity – a system fundamentally unchanged since the 19th century.

However, as global water and plumbing industries are discovering, there is clear evidence that the system is showing signs of stress due to significant reductions in drainage flow.

Global warming concerns and water shortages create problems of their own.

These problems are compounded by government water-saving strategies, together with more recent moves to reduce plumbing costs, such as reducing the venting requirements and changing the design of drainage connections.

In Australia, lower drainage flows have been brought about by reducing water use to counter the effects of enduring drought. Such reductions also compensate for a lack of investment in water infrastructure to meet the demands of growing cities.

The focus has remained on reducing the performance of various fixtures (toilets, faucets, showers, etc), with insufficient consideration given to the effect on the overall system.

A salient example of the importance of matched plumbing design is the Hong Kong SARS pandemic, which brought about big design changes in plumbing.

The 2003 report by the World Health Organization (WHO) found inadequate plumbing to be the most likely contributor to the spread of SARS in residential buildings – as well as several other infectious diseases around the world.

The push to improve the water efficiency of household appliances and plumbing fixtures has brought about substantial reductions in water use in most Australian cities, attracting the interest of many other countries.

Australia is committed to even greater water savings for toilets, faucets and other point-of-use fixtures. However, a study is urgently required to investigate the influence of toilet flush volumes of less than 4.5/3L (1.2/0.8 gallons) on existing drainline systems complying with the AS/NZS 3500 Standard.

The growing uptake of graywater and blackwater recycling systems has further affected drain lines by compromising engineered drainage systems in dwellings and commercial buildings.

Some Australian States have proposed amending building codes to allow for separate graywater and blackwater drainage systems in dwellings, a notion that has rung some alarm bells.

In Australia, New Zealand and many other countries there is little evidence of adequate research and testing to confirm the long-term effect of such changes.

In the latter half of 2007, the Australian and New Zealand Plumbing Regulators Forum (NPRF) met to consider the issue, and agreed to develop a study program for which funding would be obtained.

The project – Australasian Scientific Review of Reduction of Flows on Plumbing and Drainage Systems (ASFlow) – is in the process of finalizing the briefing paper.

NPRF technical advisory committee chairman Jeffrey Clark, who represents the South Australian Water Corporation, believes that some intervention is justified.

“We are concerned that if flushing volumes for toilets are further reduced, there could be implications for our internal plumbing systems as well as external infrastructure. This would affect the way Australian Standards are written – they would need to be substantially changed.”

Clark doesn’t think we have gone too far in our attempts to save water but he believes trials are justified to ascertain to what extent the reduction adversely affects plumbing.

“In South Australia we’ve had issues with commercial plumbing systems causing blockages. We’ve also had issues with waterless urinals and other such systems. We have made some changes in the current amendments to AS/NZS 3500 to better protect the drainage system.”

The main problem with urinals that do not use water is the build-up of uric acid, which blocks the urinal trap and drain pipe.