In the past few years, studies have been carried out to record and analyse the consumer behaviour of manual dishwashing. Manual dishwashing in households is performed in many ways that influence the use of resources. Furthermore, knowledge has been gained on the basis of experiments on how to optimize the use of resources in manual dishwashing. Optimization here means achieving the best possible cleaning performance with a minimum input of resources. This experimental knowledge, combined with the experience of everyday life, was transferred into Best Practice Tips. The aim of this study is to verify whether it is possible to save resources while applying these Best Practice Tips in comparison with the consumers' previous behaviour. In a laboratory study, 53 consumers from Europe (23 Germans, 30 other Europeans) were asked to apply the Best Practice Tips while washing up 12 place settings of dishes. The data gained were compared with that of previous studies recording consumers' everyday behaviour while washing up the same amount of dishes. The sample consisted of 113 European consumers and the sample of the second study consisted of 60 Europeans. On average, the 53 test participants applying the Best Practice Tips used around 60% less water, 70% less energy and 30% less detergent compared with the average everyday behaviour the other subjects used. Additionally, they achieved a slightly better cleaning result. An evaluation questionnaire showed that the Best Practice Tips were, in general, highly accepted; however, some concerns were given about their exact application in everyday life. Because of the wide variation of washing‐up habits and resource consumption among individuals, the confidence intervals of the studies are rather large. The results should therefore be seen as tendencies on how resource savings are possible when people are trained how to optimize resources in manual dishwashing. Nevertheless, this study should be the basis for further ones in which the learning is verified in everyday life and over a longer period of time.

The focus of this paper is to show an approach on how to optimize manual dishwashing. After presenting the method developed for simulating a repeatable manual dishwashing process, the report shows the results of the experimental study exploring the main impact factors for the optimization of the water consumption by applying a mathematical regression model. These experiments demonstrate that the water changes in the main washing bath and the water changes in the rinsing bath are significantly affecting the cleaning performance of the dishes. Concentration of cleanser is found to have a negative quadratic effect, and the interaction effect of the number of water changes in the rinsing bath with the amount of detergent (respectively Concentration of cleanser) is found to be significant. As an explanation of this behaviour, it is suspected that soil particles are transferred through foam residuals, which are not washed off in the rinsing bath. Because of several restrictions, such as having limited statistics and having excluded possible impact factors, the developed model aims at depicting tendencies of the impact factor effects and may not be generalized.

Automatic dishwashing has been optimised in manifold ways during the last decades. But it is also necessary to optimise manual dishwashing, because almost every household still washes up at least a few items by hand. A procedure based on an experimental multi-factorial laboratory study was developed to wash up a specified number of dishes with good cleanliness and an optimum water consumption as results. This procedure was then translated into generalised dishwashing tips – called Best Practice Tips. These tips were used to run two comparative consumer laboratory studies: the first part of each study investigated the everyday dishwashing behaviour and resource consumption of consumers. The second part studied the behaviour and the resource consumption after a training on the Best Practice Tips. The comparison showed that with a larger number of dishes, relevant amounts of resources of energy and water can be saved, whereas with a smaller number of dishes, no significant reduction was found. This is possibly due to a different optimum for washing up only a few items.

Investigations on the consumer behaviour of manual dishwashing have shown that there is a large variety of ways of how to wash up by hand, and the corresponding resource consumption is affected accordingly. In order to reduce resource consumption in manual dishwashing while achieving an acceptably good cleaning result, Best Practice Tips have been established (published in Fuss et al.) on the basis of laboratory experiments and the knowledge of everyday behaviour. This study is aimed at verifying the potential to save resources in real life when consumers are applying Best Practice Tips for manual dishwashing. A 4‐week in‐house study was run in two European countries, and data of the manual dishwashing behaviour were acquired before and after training on the Best Practice Tips. The results of both periods were compared with each other and between the countries. The test participants in Germany needed approximately 30% less water and 40% less energy, on average, in the period in which they applied the Best Practice Tips; in Spain, nearly 50% less water and 60% less energy for dishwashing in the period after the training. It has to be taken into consideration, however, that individual savings are very different due to specific living conditions, household sizes, practices in dishwashing and more or less prejudice against the Best Practice Tips.