This paper presents the findings of an 18-month study of detritus accumulation at two siphonic rainwater drainage systems installed in a building in Edinburgh. Findings are based on an analysis of data recorded from the site, and are positioned within the context of enhancing representation of the outlet loss coefficient used within both steady-state design calculations and finite-difference-based unsteady flow modelling techniques. The scope of findings reported herein is extensive but, in the main, shows how detritus accumulation not only builds relatively rapidly but also that 'wash-through' or 'displacement' occurs. Further, data suggest that detritus accumulation in the gutter, that is either wind-blown or is introduced from roof runoff, can, and does, build around the outlet with only relatively low intensity rainfall but that high-intensity rainfall events do seem to result in a direct and significant increase in blockage. An indication of the impact upon performance, assessed using simulation software, is also presented. Practical application: This paper reports patterns of detritus accumulation at on-site siphonic rainwater outlets. Changes in detritus 'categories' are mapped to corresponding weather data and conclusions drawn on influencing factors. The paper therefore yields key information for building owners/operators on the extent of detritus accumulation at siphonic system outlets. Outcomes also inform designers of the potential shift in loss coefficient and flow performance post-installation.

The design of domestic cold water systems is inherently based upon the fixture unit or demand unit method. Therefore, it is fundamentally necessary to understand these water demand units and how to interpret them in order to design efficient water systems that enable a balance between capital cost (where oversizing leads to elevated capital cost) and engineering good practice. Recent sustainability initiatives aimed at reducing water usage encourage the uptake of devices such as flow limiters, spray and percussion taps and low flow appliances and have driven peak water demands down in buildings. Maintaining water movement within the cold water system prevents overheating and helps to maintain a healthy hygienic system. Stagnation exacerbates overheating and may contribute to contamination by micro-organisms. To promote movement of cold water within pipework systems there has been a recent move towards adopting strategies that were not traditionally incorporated into cold water pipework design such as, a secondary cold water return circuit and end of line solenoid flush (dump) valves. These are an added expense, contribute to wasted water or energy and should therefore be carefully considered when incorporating into domestic cold water systems taking cognisance of the other contributory factors such as the building water usage and turnover, building air tightness standards and sanitary ware specification. Also water conservation in buildings is another reason to have an appropriately sized system for the potential water consumption as older appliances had larger flow rates than present; this subsequently has a knock-on-effect on the buildings drainage pipework, system selections and sizing, for example WCs. This paper presents an examination into the importance of sizing a cold water distribution system appropriately and the effect of modern building design standards on operational performance. Finally, through the experience of multiple engineers from many consultancies over several years, a summary of cold water services issues caused in modern buildings is presented and potential strategies to mitigate against excessive temperatures and promote water movement and turnover is given.