The Great Washing-Up Debate: which is better for the environment, handwashing or the dishwasher?

For many of us, washing up by hand has always felt like the environmentally responsible choice. Certainly in my household, it has been a serious point of contention, with me arguing that hand washing was the more sustainable option and my wife always wanting to fill the dishwasher. (As a point of order, it is me who does most of the washing up!)

For those of us trying to live more sustainably, it seems like a perfectly reasonable question. Why use an electrical appliance when a bowl of hot soapy water and a bit of elbow grease will do the job?

More recently, manufacturers and consumer advice organisations are increasingly extolling the environmental virtues of the dishwasher. But what is the truth lying under all the froth and bubble?

As with many sustainability questions, the answer isn't as simple as choosing one method over the other. It depends not only on what you use, but how you use it.

What Does the Research Tell Us?

One of the most comprehensive studies on this subject was carried out by researchers at the University of Michigan (Porras et al., 2020). Rather than simply comparing how much water a dishwasher uses with washing up by hand, the researchers carried out a Life Cycle Assessment (LCA).

They looked at the complete environmental impact of a dishwasher throughout its lifespan. In this case, the researchers didn't just compare how much water each method used. They also considered the energy needed to heat that water, the environmental impacts of manufacturing the dishwasher, detergents, transport, maintenance and eventual disposal.

So, what did the researchers find?

Frustratingly, for whichever side of the debate you fall on… it depends!

• For example, if you wash dishes under a continuously running hot tap, a modern dishwasher, used correctly, generally performed much better.

  
  

• In the alternative, if you hand wash in a washing-up bowl or filled sink, while avoiding unnecessary rinsing, this could result in lower life-cycle greenhouse gas emissions than an efficiently operated dishwasher in some scenarios.

Does the Manufacturing of the Dishwasher Make a Significant Difference?

Every appliance requires raw materials such as steel, plastics and electronic components. These materials have to be extracted, processed, manufactured and transported before the dishwasher even reaches your home.

The University of Michigan study included these impacts as part of its Life Cycle Assessment. Interestingly, while manufacturing does contribute to the dishwasher's overall environmental footprint, the researchers found that the energy used during the dishwasher's lifetime – particularly for heating water – accounts for the largest share of its environmental impact.

In other words, if you already own a dishwasher, using it efficiently is generally more important than the emissions associated with its manufacture.

So Which Is the Most Environmentally Friendly Way of Washing Up?

Perhaps the biggest lesson from the research is that technology alone doesn't determine environmental impact. Our everyday habits matter just as much.

If you prefer washing up by hand, you can reduce your environmental footprint by:

• using a washing-up bowl or a filled sink rather than leaving the tap running;

• washing a full load of dishes together rather than little and often;

• scraping food waste into your food waste bin or compost before washing;

• using only the hot water you need; and

• allowing dishes to air dry where practical.

Similarly, if you use a dishwasher, waiting until it's full, choosing the Eco programme and avoiding unnecessary pre-rinsing will improve its environmental performance.

Whether you prefer the dishwasher or the washing-up bowl, it's your daily habits that make the biggest difference.

As for the debate in our house? Well, I'm not sure this article will settle it—but at least I now have a peer-reviewed study to support my side of the argument!

References

Porras, G. Y., Keoleian, G. A., Lewis, G. M. & Seeba, N. (2020). A Guide to Household Manual and Machine Dishwashing Through a Life Cycle Perspective. Environmental Research Communications, 2(2), 021004. https://doi.org/10.1088/2515-7620/ab716b

Porras, G. Y. (2019). Life Cycle Comparison of Manual and Machine Dishwashing in Households. Master's Thesis, University of Michigan.