Current predictions indicate that UK rainfall severity and frequency will increase during the winter months. To avoid surcharging existing sewers we must understand the techniques necessary to attenuate and delay the peak flow discharge from any roof or catchment area within the building boundary — basically an application of the unsteady continuity-of-flow equation where inflow equates to outflow minus the rate of change of storage within the control volume, in this case the building or property boundary. This requires an understanding of the time-dependent nature of rainfall-induced sewer flows. Solutions will include intervention storage tanks that may or may not be utilised as part of a rainwater harvesting system or so-called green roofs that allow a proportion of the precipitation to be absorbed or re-evaporated to the atmosphere or, indeed, a reversal of the popular urban replacement of front gardens with vehicle parking. Other solutions available to the engineer include siphonic rainwater systems that allow a reduced number of system downpipes to remove rainwater from roofs quickly by running full bore under siphonic conditions. Such systems have been installed successfully at many prestigious buildings, including the Sydney Olympic Stadium, Hong Kong Airport and Murrayfield in Edinburgh. There is a need to translate the research undertaken in this area into useable design guides. Intervention to avoid drain surcharge will be a major constituent in our efforts to prevent localised flooding and is a contributory element in the application of sustainable urban drainage. Water shortages Water supply and conservation is a truly international issue. Estimates of the population figures without access to reliable and safe drinking water supplies are daunting. UN initiatives have consistently failed to achieve their objectives due to the scale of the problem, lack of resource and motivation and political instability in the areas most in need of support. While access to water in the 1880s may have sparked the Lincoln County Cattle Wars, in the 21st century I think I agree with the Israeli general who, when asked if water could be a cause of conflict replied: ‘It’s cheaper to build a de-salination plant.’ In the UK, along with other developed countries, water shortage is exacerbated by both local shortfalls in precipitation and by our choices as to urban location and life style. Defra proposals indicate a reduction in water usage from 150 l per capita per day to 120 to 130 by 2030. This aspiration has to be seen against a background of climate change that over the same period is expected to result, in the southern UK, in high summer temperatures and dry conditions — while extreme winter precipitation will become a normal event. In the UK, 52% of water is used domestically, of which up to a third is used to flush WCs. In commercial buildings, the equivalent figure, including urinals, approaches 60%. Government will require the input of CIBSE as the relevant engineering institution with access to reliable design methods to assist in setting the targets for water usage. These targets will have to take into consideration both the local water resource and the local housing and commercial/industrial water needs. It may well be that the outcome of such discussions will lead to differential targets nationwide or to decisions as to re-location of population. During 2008 CIBSE will work with DCLG and Defra to deliver the awaited Part G of the Building Regulations that will offer guidance on water usage levels acceptable across the UK. Some approaches to water conservation are predicated on a change in user attitude. However as an engineer, I have a distrust of policies based on changing population attitudes and would rather base water conservation on enhanced product design to yield the same user satisfaction without the user necessarily being aware of the reduction in water use. During the 1970s Scandinavia was regarded as leading the field in efficient appliance design. However, undeniably due to the extended droughts suffered in the past decade, Australian industry has taken on this mantle. Despite WC water usage reducing internationally, a time traveller present in 1900 at the discussions between the Metropolitan Water Board and the appliance manufacturers aimed at reducing flush volume from 40 litres, who then moved forward to London in 1998 to attend meetings of Defra’s Water Regulations Advisory Committee, would have been amused at two things that would not have changed over the hundred years — the speed of travel across the capital and the arguments put forward by the manufacturers to resist reductions in flush volume. Water conservation is a continuing issue that will require CIBSE’s involvement into the foreseeable future and also require an understanding of the possible consequences of such initially attractive schemes as grey water re-use on the system as a whole. For example, whether replacing the quasi-steady discharge from baths — relatively efficient sources of waste transport in the building drainage network — with an equal volume delivered in a series of rapidly attenuating WC flushes remains to be evaluated. This article is based on part of Prof. Swaffield’s CIBSE presidental address ‘Living with the albatross’.