Who is more economical: dishwasher or human?

For a long time, it was said that the dishwasher was superior to manual washing up in terms of energy and water consumption. But blanket statements on this are wrong

What is more sustainable – dishwasher or hand washing? In the kitchens of environmentally conscious people, this question repeatedly causes heated discussions. Or worried. Because since 2011, the question seemed to have been finally clarified. This year, a study by the University of Bonn was published that dealt comprehensively with the washing behavior of the common European. The result: dishwasher beats man. An average of 50 percent of water could be saved compared to washing up by hand – and 28 percent of electricity.

In a previous study from 2004, the Bonn researchers had already shown "that a modern dishwasher usually delivers better washing results with significantly lower water consumption and time commitment".

There is also energy in the dishwasher

But there was also criticism of the studies. For example, the Oeko-Institut in Freiburg criticized the fact that the researchers had not taken important items into account in their balance sheet. For example, the energy that has to be used to manufacture and transport the device, the so-called grey energy. According to the Association of Energy Consumers, it is around 1000 kilowatt hours, which corresponds to about the electricity consumption of 1000 wash cycles.

The Bonn researchers also failed to take into account the fact that energy sources are harmful to the climate in very different ways: Electrical energy is the most climate-damaging form of energy due to conversion and transmission losses. And the combustion of gas releases only about a third of the climate-damaging CO2 emissions compared to electricity – with the same heating capacity.

Marjo/Colourbox — Five simple steps for a more sustainable life

An important point. Because every dishwasher works with electricity. But hand washers use a wide variety of energy sources and appliances to heat water, including electricity-powered hot water tanks (low efficiency, high emissions) or gas instantaneous water heaters (good efficiency, low emissions).

The cleaning agent was also disregarded: While the dishwasher has to work without a brush, but with aggressive chemicals and phosphates that damage water, the hand dishwasher can use gentle and biodegradable detergents.

Not machines, but people are economical

Incidentally, the decisive objection to the blanket statement that the dishwasher is superior to cleaning by hand was provided by the Bonn researchers themselves – as early as the 2004 study.

They reported on their 113 test hand washers: "In one extreme case, the test person only rinsed under running, hot water and dosed the washing-up liquid directly onto the dishwashing sponge, in another the test person placed the washware parts one after the other in up to four rinsing baths (soaking, pre-cleaning, main cleaning and rinsing)." The different strategies for washing up also explain the striking ranges in consumption: Hand washers consume between 0.2 and 16.6 kilowatt hours and 14 to 447 liters of water.

Dishwashers, on the other hand, need between 1 and 2 kilowatt hours and between 15 and 22 litres of water for the same amount of dishes. The "arithmetic mean" calculated by the Bonn researchers may therefore be higher than for the dishwasher. But because absurdly wasteful behavior has also been included in these average values, both are probably correct: that the efficiently used dishwasher is superior to haphazard hand washing. And that the (smart) washing up by hand can be more economical than the averagely efficient dishwasher.

The real message of the 2011 study is that many dishwasher users simply can't handle their machine.

Tips for washing up

Do not let food residues dry in the first place - or soak them before rinsing.
Sort the dishes and start with the least soiled.
Do not use more detergent than necessary (dosing instructions).
Drain washed dishes (the heat stored in the dishes will cause them to dry on their own).
If you use a dishwasher: Do not pre-rinse by hand.
Do not turn on the dishwasher until it is fully loaded. The "Half Load" button (if available) often saves only 10 to 20 percent of electricity and water.
To minimize standby consumption, you should switch off the device after the end of the program.
For light soiling, economy or short programs at temperatures of about 40 to 45 degrees are also suitable: This protects the dishes, saves water and up to 20 percent electricity.