Usage of dishwashers: observation of consumer habits in the domestic environment

Over the years, appliance manufacturers have been successful in developing dishwashers that enable consumers to save time, energy and water very conveniently. Within the last 20 years the savings in energy consumption exceed 30%, and the average water consumption per cycle has been more than halved. As a result, it is very hard for the majority of people to compete with the efficiency of a dishwasher when dishes are done by hand. However, consumer habits (e.g. regarding the use of the dishwasher load capacity, programme choice and particularly the additional pretreatment of dishes with water) are influencing the overall efficiency of the dishwashing process and resource use. Still, detailed information on consumer behaviour in everyday life concerning these issues is rare. In order to improve the understanding of dishwashing habits and to fill the lack of information about dishwashing on the household level, an in-house consumer survey in four European countries (Germany, Italy, Sweden and the UK) was conducted between 2007 and 2008. Two hundred households with and without dishwasher were interviewed and comprehensively observed. For a period of 2 weeks, participants recorded every dishwashing process with the help of a dishwashing diary and pictures they took of their loaded dishwashers. In addition, an in-depth observation took place in 82 households where measurements and webcam observations were recorded at the kitchen sink. Actual resource consumption data for manual dishwashing and the pretreatment for the dishwasher were obtained. The present paper reports on findings of this investigation and concentrates on consumer habits related to the use of the dishwasher. In general, the study showed that the households with dishwasher used on average 50% less water and 28% less energy per cleaned item compared with households not owning a dishwasher. Yet, there were still consumer habits, which indicate that a higher degree of sustainable dishwashing is achievable. The researchers found that in 20% of the dishwasher cycles, baskets were only slightly filled and consumers were likely to use higher amounts of energy than stated on the energy label because they have chosen mostly in favour of high cleaning temperatures (52% used 65°C and higher). Particularly in Italy and Sweden intensive pretreatment habits have been observed, resulting in an average additional water use of 11-20 L per dishwasher cycle.