Manual vs Machine Dishwashing
Which is better: hand washing dishes or machine washing dishes? It turns out that with the correct technique, hand washing dishes performs the same or better across a variety of parameters.
I am sure you have many questions on how this can possibly be, especially given the general consensus that dishwashers are great water and time saving devices.
Bottom line:
If you are not ready to review your dishwashing practices in order to reduce green-house gasses (GHG), continue to use the dishwasher and dishwashing powders.
If you have 8 minutes to spare per full dishwasher, you can reduce GHG emissions by 22-30% by hand washing your dishes.
I have listed a series of questions and their answers below. You are welcome to read all the information in full in the academic articles I name as Study A, B, C, and D throughout this post (also see full references and download links at the end of this post).
What does being ‘better’ mean exactly?
Using less water, less electricity, less raw resources (eg steel), less environmentally polluting materials (eg plastics), less waste production, which together result in overall less GHGs (eg carbon dioxide) over the average 10 year lifetime of a dishwashing machine.
So what about all those claims that dish washing by hand wastes a lot of water?
Study A tested three manual dishwashing styles and eight dishwasher cycles and compared their impact in terms of GHGs across two user scenarios. In scenario 1: users were left to do dishes manually and load dishwashers as they wished. In scenario 2: users were taught recommended machine dishwashing loading/use and recommended hand dishwashing procedures.
Here are the results:
Scenario 1 – users left to their own devices (without education)
- Hand dishwashing of any sort produces more GHGs than machine dishwashing. If not taught how to do the dishes correctly, manual dishwashing produces 2.7 times more CO2 than dishwasher use.
Scenario 2 – users are taught recommended machine dishwashing loading/use and recommended hand dishwashing procedures (with education)
- Recommended best practice manual dishwashing procedures improve scenario 1 manual dishwashing GHGs emissions by 249%. Best practice manual dishwashing produces 22% less CO2 compared to best practice dishwasher loading/use over the lifetime of a dishwashing machine (10 years).
I bet the best practice manual dish-washing technique is weird and inconvenient. Is it?
This is a matter of trying it for yourself… perhaps over the new year holidays given they are just around the corner?
I didn’t find it weird or inconvenient at all and it has improved my manual dishwashing water usage from 17 litres [4.5 gallons] for all the dishes and pots that my dishwasher can hold, to 10 litres [2.6 gallons] for the same amount of dishes and pots.
I use my dishwasher as a giant air drying rack. Here is what it looked like after I did the dishes by hand using 10 litres of water…
… and here is the recommended best practice manual dishwashing method (click the image to download printable version):
Study A, manual washing vs machine washing, included the GHG’s of machine laundering your tea towels at least once a week. I will add, to kill bacteria and pathogens, you should launder your dishwashing sponge and bench wiping cloths at the same time as the tea towels, washing all at temperatures above 70°C [160°F].
Do the dishes really come out clean with the recommended manual dishwashing method?
Yes they do.
I tried it and my dishes/pots/glassware/cutlery was as clean as they have ever been. Study A tested this aspect scientifically and reported dishes were as clean as per machine dishwashing.
What about pathogens and bacteria on dishes/sponges/benches/tea-towels?
The study that produced best practice manual dishwashing pictogram, washed dishes in 60°C [140°F] water, but in Australia domestic hot water temperature delivery is capped at 50°C [120°F] to prevent burns and scolds.
A minimum temperature of 65°C [150°F] is recommended to kill bacterial and pathogens, so I understand if you are concerned about pathogens and bacteria surviving on dishes and the like, bench surfaces, and sponges after manual dishwashing.
Study B reported that whilst sponges and tea-towels often became contaminated “transfer from dishes onto food was rare” (page 213). Additionally they recommended “frequent replacement or decontamination of tea towels and washing-up sponges” (page 224); that’s what laundry at 70°C [160°F] or higher once a week would do.
If you can’t be bothered to machine launder your tea towels/sponges/bench wiping cloths, then machine dishwashing will likely be more sanitary for you.
Doesn’t the manual dishwashing method leave soap residue on the dishes/pots/cutlery/glassware?
Both manual and machine dish-washing leave soap residue on various items washed with their respective soaps, and these soap residues are indeed transferred to the food we eat off our plates.
The residue left on dishes using typical dishwashing liquid and typical machine washing powders have been tested for toxicity to humans and have been found to have extremely low toxicity when ingested by children and adults alike.
If you would like to read more about this aspect see studies C and D.
This is all well and good but doesn’t manual dishwashing take so much longer than loading a dishwasher and walking away?
This depends on how efficient you are at washing the dishes or loading your dishwasher, and on how much you value 8 minutes of your time. Study A compared this aspect of dishwashing too.
The fastest participants took 30 minutes to do a load of dishes by hand vs 6 minutes to load a dishwasher (24 minutes saved using a dishwasher machine).
The slowest participants took 52 minutes to do a load of dishes by hand vs 22 minutes to pre-rinse and load a dishwasher (30 minutes saved using a dishwasher machine).
But if like me, you are very fast at manual washing (taking 30 minutes) but very slow at pre-rinsing and loading a dishwasher (taking 22 minutes), lowering your GHG emissions only takes an extra 8 minutes of your time per full dishwasher.
What about those super water efficient dishwashers which use only 6 litres [1.6 gallons] of water? Can manual washing use less water than that?
The answer is yes. I have devised a method of using only 4 litres [1.1 gallons] of water to do all the dishes/pots/cutlery and the like that fit in my dishwasher.
If I receive enough requests on how to achieve this I will upload the video.
References – websites accessed and correct at time of publishing
For Life Cycle Analysis study of manual vs machine dishwashing [Study A]:
Porras, Gabriela Y., Gregory A. Keoleian, Geoffrey M. Lewis, and Nagapooja Seeba. “A guide to household manual and machine dishwashing through a life cycle perspective.” Environmental Research Communications 2, no. 2 (2020): 021004.
go to the following address then click on ‘read full text’ button: https://www.researchgate.net/publication/339222159_A_guide_to_household_manual_and_machine_dishwashing_through_a_life_cycle_perspective
For pathogens and bacteria contamination of dishes/sponges/tea towels [Study B]:
Mattick, Karen, Karen Durham, Gil Domingue, Frieda Jørgensen, Mithu Sen, Donald W. Schaffner, and Tom Humphrey. “The survival of foodborne pathogens during domestic washing-up and subsequent transfer onto washing-up sponges, kitchen surfaces and food.” International Journal Of Food Microbiology 85, no. 3 (2003): 213-226.
go to: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.727.3109&rep=rep1&type=pdf
For toxicity of manual dishwashing liquid residue on dishes [Study C]:
Yost, Lisa J., Joseph D. Rodricks, Duncan Turnbull, Paul C. DeLeo, J. Frank Nash, Antonio Quiñones-Rivera, and Pete A. Carlson. “Human health risk assessment of chloroxylenol in liquid hand soap and dishwashing soap used by consumers and health-care professionals.” Regulatory Toxicology and Pharmacology 80 (2016): 116-124.
go to: https://www.sciencedirect.com/science/article/pii/S0273230016301611
For toxicity of dishwasher machine powder residue on dishes [Study D]:
Cressey, P., and I. Pattis. “Health risk assessment: Dishwasher powder.” Institute of Environmental Science and Research NZ (2014).
For best practice manual dishwashing see:
Fuss, Natalie Anna. PhD Dissertation: Determination And Verification Of Possible Resource Savings In Manual Dishwashing. Bonn University, Germany (2011)
go to: https://bonndoc.ulb.uni-bonn.de/xmlui/handle/20.500.11811/4740
For lowest temperature recommended to kill bacteria and pathogens:
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