A lot of drama revolves around doing the dishes. Who enjoys doing them? Maybe you are lucky to call yourself the owner of a dishwasher. Regardless, they need to be done.
I am not the lucky one. You know, there’s actually a pile of dishes waiting for me right now. But that’s okay, I somehow like doing them.
Sometimes, I ask myself whether we should get a dishwasher. You have probably heard that they use less energy and water than doing the dishes by hand. But is that really true?
What others say about it
- Treehugger says: it depends.
- Paul Wheaton says that washing dishes by hand is better than using a dishwasher
- telegraph & cnet think that dishwashers are the answer
- sciencealert & The Washington Post urge us to stop washing dishes by hand
Notice the dates when those articles got published. Technology advances and dishwashers improved in the last 10 years. The first three articles already need reevaluation. But I also don’t want to blindly trust the other sources but rather verify.
So I set myself up to get to the bottom of this.
Why am I doing this?
Sara and I are heading into a self-sustainable life. This means that we are responsible for collecting our water and generating our own electricity. Two very precious resources we have to use with care.
Reading the pro-dishwasher articles I noticed, that they mostly focus on how much the dishwashers improved. In addition, they compare with a human who performs badly. Also, they have not considered that kitchen taps got upgrades over time, too. Just two weeks ago we bought a tap that supposedly uses 30% less water. Well, we actually bought it because it seems more practical than our old one, which broke. The water savings is a nice plus though!
In my test, I am going to set the focus on the following points:
- water & electricity usage
- smart vs dumb usage
In order to fairly compare efficiency, I am going to base the test on cleaning a 12 place setting (EN 50242). This includes a total of 140 individual pieces (49 plates, 24 cups, 64 forks/spoons/knives, 3 bowls).
Before starting, however, there is one important question to answer.
Should I use hot water when washing by hand?
The common belief is that dishes need to be cleaned with hot water. In short: yes, hot water is in general better than cold. Let’s break it down.
Rests of food, especially fats, come off easier when washed with hot water. Oil and grease melt at around 40 °C, making it a breeze to scrub off
However, starch and uncooked proteins such as raw egg, are easier to remove under cold water. At higher temperatures, starch tends to clump. Raw protein cook and tend to stick harder to the surface.
Those pesky germs
Most bacteria start to die off at temperatures above 60 °C. However, a normal person, can’t take water temperatures above 50 °C. Therefore, washing dishes by hand with cold water will be as effective as hot water.
This is a clear win for dishwashers as they easily go up to temperatures above 60 °C, effectively killing most of the bacteria.
Luckily, dish soap does a good job removing germs, which mostly live within the food rests. Soap, unless antibacterial, does not kill bacteria but helps washing it away. When cleaned well, what’s left may be some bacteria stuck on the plate. Most of them will starve to death. One should be rather concerned about the kitchen sponge, which is a paradise for germs. So make sure, that you keep it clean and replace it every so often.
Using hot water reduces the time the dishes need to dry on the rack. The warm water evaporates quicker and it’s said that you’ll also have fewer streaks.
In conclusion, hot water is not needed but makes things a little easier. For our comparison, we will keep both styles in mind.
Water & energy usage
Our future home won’t depend on the water and electricity grid. We will collect both things ourselves and need to be conscious of how much we use it.
For our test, we will distinguish between the following:
- dishwasher full vs half full
- washing up by hand with hot water vs cold water
Engineers are constantly improving, making dishwashers more efficient. I took a look at stats of the latest models. I found that on average dishwashers use 10.2 liters of water and 0.93 kWh of electricity.
The absolute winner is this machine only using 3 liters of water as the crazy outlier.
Not having to wash up by hand will also save you a lot of time. All that needs to be done is to put the dishes inside the machine, put in the cleaning product, start the machine, take out dishes when done and dry.
As mentioned earlier, dishwashers have the great advantage of being able to heat the water to temperatures that can kill most the of pathogens that reside on the dirty dishes. The end result is pretty sterile plates and glasses.
Washing dishes by hand
On average, a person spends 0.7 to 1.1 hours a week washing up. Some have mastered their trait while others don’t even get the basics right. The amount of water and energy used varies greatly from person to person. Based on cleaning a 12 place setting, this study found that on average we use about “103 liters of water, 2,5 kWh of energy and 79 minutes time”.
I have also set out to throw myself into the ring and measure my own water and energy use.
Over the last weeks, I’ve been measuring how much water I use for cutlery, cups, bowls, and plates. While having my personal study in mind, I kept on washing up as I always do.
My personal style
First some ground rules:
- leave very dirty dishes soaking overnight
- only open tap when needed
- open tap only half way
The way I wash up goes like this:
I make sure that each dish I tackle is fairly well rinsed. If they are not, I give them an extra quick rinse, maybe scrub off sticky bits with my hands. After that, I scrub them with the sponge until clean.
Usually, I accumulate many cleaned dishes in the sink before I rinse them. This way I can leave the water running while putting one dish on the rack while holding the next already under the water stream. Should I feel that I need more time to place the dish on the rack, I stop the running water. This is a habit I developed over time. I am not even thinking about it anymore.
Until all dishes are cleaned, I repeat this procedure.
Unfortunately, I was not able to get a 12 place setting together every time I did the dishes. Instead, I broke the dishes down into categories and took averages:
|type||per unit||in a 12 place setting|
|plates||0.21 L||10.22 L|
|cups||0.24 L||5.64 L|
|cutlery||0.05 L||3.33 L|
|bowls||0.18 L||0.54 L|
In total, I use 19.74 L to wash up a 12 place setting. I still use twice as much water as a dishwasher. But compared to the results of the study, I think I can be proud of myself.
Heating water requires energy. The more water is heated and the higher the temperature difference, the more energy is used.
A typical electric water heater brings the water temperature from typically 15 °C to 60 °C.
Knowing how much water we use we can plug the values in this formula,
Pt = (4.2 × L × T ) ÷ 3600
Pt = (4.2 × 19.74 × (60 – 15) ÷ 3600 = 1.04 kWh
The result looks very good but I believe that this formula disregards efficiency. Electric water heaters have an efficiency of 86 to 93 percent. Let’s assume ours is not as good and therefore uses 1,21 kWh.
And there we go, I am using 1.21 kWh to wash up a 12 place setting.
As we already found out, we cannot get water temperature high enough to kill off bacteria. But we also found that it is generally okay, to use cold water.
I personally, only use warm water during the colder months for obvious reasons. In Spain, this is usually between December and March. During the summer months, the colder the water is, the better.
That makes only 4 out of 12 months I am actually using the water heater. On average reducing energy use by 66 %. In my case, that means I use only 0.4 kWh on average in a year.
So, which one is better?
Having researched all this data, we are now able to objectively compare:
| by hand|
|Water||10.2 L||20.4 L||103 L||103 L||19.74 L|
|Energy||0.93 kWh||1.88 kWh||2.5 kWh||0.83 kWh||0.4 kWh|
|Cleanliness||super clean||super clean||fairly clean||fairly clean||fairly clean|
On the other hand, one can argue that some people even don’t know how to load a dishwasher correctly, hence making them perform twice as bad.
Simply not washing up with hot water in the warmer months already requires the same or less energy as the dishwasher.
I started this test believing that I will miserably fail against the dishwasher. After all, most articles made it painfully clear how much better the machine is. It turns out that it’s not that simple.
Yes, I use twice as much water, but half as much energy. And in my case, I think energy is more valuable than the water. So I am very happy with my performance.
In fact, if you use cold water in the warmer months like I do, you could use up to 45 liters of water. And you would still use the same amount of energy as the dishwasher.
That being said, I learned that buying a dishwasher can also be a good choice. Be it, that one seriously lacks washing skills or has a real health issue with hand washed dishes. I haven’t heard of the latter though.