This text is taken from the Courrier de la Planète. Click here to subscribe.
Is it better to wash the dishes by hand or in the dishwasher? It may be a debate at the family table or in the office between colleagues: machine washing or hand washing, which has an advantage for the environment when it comes to cleaning soiled plates, bowls and cups?
The answer is not so simple. It is necessary to calculate the water and energy consumption of the device, not only during its operation, but also during its initial production and at the end of its life.
As for water consumption, the debate is quickly settled: a washing cycle in the dishwasher consumes 10 to 20 liters of water, while running the dishes under the tap for five minutes requires 25, depending on the Climate and Energy Transition Office of the Quebec Ministry of the Environment.
For a device to obtain Energy Star certification, water consumption is also the strictest criterion: certified dishwashers must use 30% less water than “classic” models.
A team of American researchers has decided to get to the bottom of this debate by comparing several washing methods and taking into account the life cycle of the appliances. She asked 38 people to fill a dishwasher like they would at home. Another group of 37 participants had to manually wash the dishes according to each person’s habits.
It should be noted that this study was partially funded by Whirlpool, but entirely conducted by independent researchers at the University of Michigan.
Their peer-reviewed findings were published in 2020 in the journal Environmental Research Communications. The overall verdict: A properly used dishwasher produces fewer greenhouse gas emissions on average in the United States, compared to a “typical” hand wash.
hot water energy
“Consumers have a lot of influence on their ecological footprint, through the products they consume,” says Gregory Keoleian, one of the researchers who conducted the study and director of the Center for Sustainable Systems. Systems) from the University of Michigan.
It should be noted, however, that these results are more valid for the United States, but less so for Quebec, because the calculated footprint depends largely on the type of energy used. However, hydroelectricity, which represents 97% of all electrical energy consumed in the province, has a negligible impact on the environment compared to the energy used in the American scenario taken into account in this study.
In comparison, hydroelectricity represents only 6% of the national average of electrical energy sources in the United States, coal, almost 22%, gas, 38.4%, and nuclear, 19%.
But beyond the type of energy used, “behaviours also matter a lot,” says Keoleian. In this particular study, participants washed dishes by hand using a two-tub or two-sink method. This involves first immersing the plates in hot water, to scrape off stuck-on food or to let them soak. In the second basin or sink, we only rinse the dishes with cold water, which we then leave to dry in the open air.
It is in fact this method that produces the lowest GHG emissions in the American context. “But it’s only if you’re a good scrubber, specifies the researcher, which is really not given to everyone. In the exercise conducted in the laboratory, only 16% of the participants had indeed used this way of doing things, compared to 41% who had washed the dishes under running water, leaving the tap running, the method which shows the worst results. .
Dishwasher use habits are also very important. The habit of rinsing the plates before filling the device “is tenacious”, since 74% of the participants did it, explains the expert. However, it does increase emissions by 3%.
Turning off the warm air drying option reduces the impact by 11%, according to this study. The initial impact of the production of the dishwasher in the factory was amortized over a period of 10 years, according to a routine of four washes per week. “Dishwashers typically last between 10 and 13 years,” says Keoleian.
Performance standards are “increasingly stringent” in relation to energy and water consumption, he adds, hoping they will continue to improve.