Issue: 5/01

Two hundred years ago, Wellington, a British general famous for defeating the French in the Peninsular War and later at Waterloo, defined the role of military intelligence as the ability to "see over the hill." This could also apply to university research within the industry. In plumbing system design, it is necessary to identify the pressures driving innovation and the impediments to innovation. We need to identify and prioritize the major challenges facing the industry so research can focus on assisting designers, appliance manufacturers and code specifiers. To some extent, these priorities are national; however, there are international imperatives that dictate medium- to long-term research.

We may postulate a three-phase approach:

    1. Identify issues requiring research;

    2. Formulate solutions based on research undertaken with either government or industry funding, or preferably both; and

    3. Disseminate research findings in a form that will find acceptance by the national and international code bodies.

Identifying Water Conservation as a Research Issue

While the Drainage Research Group at Heriot-Watt would identify water conservation as the underlying theme for future research (as it affects the whole spectrum of design), it would also be interesting to have readers of this column propose their leading contenders. We could pick these up in a later column.

It is true that reduced water usage governs the design of w.c.'s and other appliances, ranging from low-flow showers to dishwashers and washing machines. It dominates drain sizing, leading to reductions in the drain cross-sectional area or the adoption of alternative drain cross-sections, and affecting solid transport and system maintenance costs.

Water conservation also increases the sensitivity of the drainage network to installation defects. Shallow gradients, susceptible to slope defects, may have been acceptable if the system flows were appreciable, but reduced flows will exacerbate deposition and eventual blockage. Reduced water flows will also reduce the need for system venting, saving materials and design and installation expenditure.

Developing Research Activity

The second phase of approaching research on water conservation, formulating solutions, requires action by both industry and research groups.

Understanding the effect of water conservation on solid transport and drain sizing requires a sound knowledge of the fluid mechanics of the transport process. Laboratory testing alone will not be an affordable option due to the scale of the networks to be simulated and the need to be able to "play games" with design options in order to identify which is most appropriate. W.c. discharge profiles and joining flows at junctions have to be incorporated into any analysis of solid transport under water conservation criteria. Simulations have been developed and made available to the industry that can be used by forward-looking companies to address these issues. Such simulations need wider acceptance; the research objective would be the establishment of networks to disseminate current research and provide routes for discussion.

Installation standards are a difficult and sensitive area. Trends in the U.K. have moved away from the traditional apprenticeship schemes that led to recognized levels of operative expertise. Simulations can incorporate defect situations and could be used to investigate the sensitivity of proposed designs. Such research would require the involvement of designers, clients and installers.


Venting is an area with enormous potential for research activity that would lead to improved design. Water conservation will reduce vertical stack surcharge and positive air pressure transient propagation. While trap seal retention will remain the essential aim, reduced water flows can reduce the danger of traps being lost due to positive system pressures or the traditional induced siphonage caused by high suction pressures. Stack diameter could also be reduced, along with the reliance on branch and relief venting. The acceptance of air admittance valves would be easier if the likelihood of system air pressure surges was reduced. The removal of roof penetration as a standard venting practice could have profound effects on system design and operation.

Again, simulations exist that are based upon the fundamental equations of pressure transient propagation. The challenge is to convince the industry, particularly design practices and code authorities, that such simulations accurately represent the situation within drainage and vent systems subjected to low amplitude air pressure transient propagation.


Rainwater drainage is often neglected, even as buildings increase in complexity and the climate shifts. Despite political wish fulfilment as to the acceptance of scientific data on global warming, there is a need for alternative solutions to roof drainage and to the loads placed upon urban drainage networks due to heavy rainfall on paved and drained areas. Siphonic rainwater systems are gaining acceptance in Europe for many large buildings, and the simulation of the system operation will be necessary to assist designers in the specification of systems capable of dealing with our changing climate. Similarly, delaying mechanisms that even the load on urban drainage are being investigated in Europe under the blanket title of sustainable urban drainage.

Finally, the behavioural aspects of building drainage usage require attention. Water usage data needs to be much more detailed. There is a need to investigate and record the usage pattern of appliances in both domestic and commercial environments. This data is essential if realistic estimates of drainage flows are to be determined and realistic simulations of drainage system operation developed.

Industry Cooperation

While this coverage of likely research areas may appear diverse, the topics identified share two main characteristics. Firstly, they are driven by economic or climatic criteria--water conservation on one hand and the increased likelihood of intensified localized rainfall on the other. And secondly, the main research thrust in each case involves simulation development and the gathering of reliable usage data. In all cases, the required research cannot progress without the full support and commitment of the industry, whether represented by appliance manufacturers, singly or through trade associations, or design practices, again singly or through enlightened professional institutions. Thus, simulation development and usage data gathering are the major research needs.

Convincing Code Bodies

There remains the requirement to disseminate findings in such a way that they are acceptable to code bodies at a national or international level. Currently, we are involved in two major code body discussions--one in the U.K. and the other overseas. The U.K. example is interesting, as it highlights the conflict between the politically desirable and the engineered possible.

At present, legislation in the U.K. features "adoptable" sewers, or sewers that become the responsibility of the privatized water companies, hence removing the direct cost of maintenance from the householder--an attractive political objective. In the past, these adoptable sewers have been defined in terms of their diameter, i.e. not less than 6-inch. One strategy to deliver universal adoption would be to ensure that all dwellings were connected to the sewer via 6-inch diameter building drains. However, this blanket solution, while politically attractive, could lead to severe deposition problems due to the low flow expected from single dwellings and future water conservation legislation.

In order to contribute to the debate, both experimental and simulation studies were carried out to determine the likely flow conditions that would be experienced in the dwelling to the lateral drain, and also in the lateral as it collects flow from sequential dwellings. International data on flow loadings were also accessed. Together, this provided the evidence that led to a modification to the proposed legislation, re-introducing a linkage between flow loading, the number of dwellings served and the drain diameter. The first lesson from this code discussion is that code bodies must be willing to accept into their membership researchers who can perhaps "see over the hill." The second is that researchers must be willing to serve on code bodies. Both require cultural acceptance.

And finally, returning to Wellington's definition, the problem was, and has been over the past 200 years, that intelligence gathering was not regarded as a high priority by those more concerned with the face-to-face execution of their profession. The "we know how to do this without being told by a bunch of theorists" attitude remains strong. Perhaps breaking down those perceived barriers is the real research objective.