Why running a dishwasher even twice a day is better than hand washing dishes

Plus why the heck does Eco mode take so long...

I used to be on team Hand Washing + 1 Nightly load of dishwashing. Now I switched to "use dishwasher as much as needed” and here’s why…

1. Less Water

A dishwasher uses less water when compare to hand washing a load of dishes. Hard to believe, isn’t it? This giant tub of appliance uses less water? Yes, indeed!

The data is clear!

A 150 participant UK study in 2007 showed that on average people used 49L of water when hand washing a full load of dishes compared to 13L using a dishwasher. Now modern appliances have bought that number down even more (11L).

Why does the dishwasher use less water? Dishwashers usually have three wash cycles: pre-wash, main wash, and final rinse. When each cycle starts, water is pumped into a small pool at the bottom and heated. This water is then sprayed through the arms to clean the dishes. The dirty water that drips back into the pool is filtered, reheated, and reused. This non-stop process of recycling the fixed amount of water for several minutes or even hours (depending on the mode) which is why they use so little water.

2. Less Energy (Eco Mode)

If you run the dishwasher on Eco mode, you can save a lot of energy costs. But you may notice that it takes a really long time (couple of hours or more)  to finish the job. How can something that takes a long time to run consume less energy? Let’s find out.

The efficiency of a typical chemical detergent is higher with higher temperatures. So, naturally you can heat up water to high temperatures that your hands will not tolerate during hand wash and get it sparkly clean, right?

But, here’s the problem….Heating the water from room temperature (say 35 C) to hot temperatures (60-85C depending on the cycle) is what sucks up a lot of energy. The eco mode tries to avoid heating the water too much in order to save on electricity costs. But how does the Eco mode clean without heating the water up? That’s where enzyme based detergents come in. These enzymes break down starches (using amylase) and proteins (using protease) that are stuck to the plates and cups. The enzymes (like the ones we have in our body, plants, yeasts, bacteria and other living things) function best between 35-45C. The enzymes do not work at high temperatures. (Remember, that this why we blanch our vegetables before freezing them. Exposing enzymes to high temperatures instantly deactivates them).

The problem with enzymes though is that they take a long time to do their job. They are good at their jobs, just that it takes longer than the “get in, get out” approach of the detergents.

This is why the Eco mode takes a long time.

Powder/gel/pods?

If you are using a powder or a gel, the amount you add can vary based on your load capacity or needs. A pod or tablet usually has detergents, water softeners (to transform hard water to soft), enzymes, bleachers, etc all rolled in one compact form. So, if you want to have 1 less decision to worry about at the end of the day, pod is your answer. But, it is expensive and can be dangerous if accidentally ingested by children, pets and tiktok users (not accidental in this category!). 

I, personally, do not like pods because I use wet hands to pick them up and they get all soggy/sticky on me. But, that’s on me. I like the liquid detergent better. It contains enzymes in the ingredients. Mine lists alpha amylase (enzyme)*, and subtilisin (protease enzyme)* in the ingredients. You can check yours.

3. Cleaner

Finally, a dishwasher is cleaner too.

A study found that hand-washed items had bacterial counts ranging from 1 to 6,000 colony-forming units (CFUs), whereas machine-washed items had counts below 100 CFUs. Additionally, using a towel to dry dishes wound up with more bacteria than dishes left to air-dry on a draining rack.

Conclusion

What are your thoughts about the dishwasher? Have you started using it more or less as time goes? Post your comments below…

Reference

Of all the research I did for this piece, this German Prof convinced me the most about its benefits.

https://researchoutreach.org/wp-content/uploads/2023/10/Rainer-Stamminger-Lotta-Schencking.pdf

He makes the case eloquently in this podcast

https://www.listennotes.com/podcasts/sliced-bread/dishwashers-vP_lBXYpRka/

I wrote about the history of dishwashers and its science recently for my Hindustan Times column (FYI: It is subscription access only)

https://www.hindustantimes.com/lifestyle/art-culture/rinse-of-the-machines-swetha-sivakumar-on-dishwashers-101719650464019.html