Christmas is gone and if you have a big family like me, after all the food and drinks served during the celebrations, you had a lot of dishes to wash. Washing dishes can take a lot of water and energy; and also a lot of your time if you don’t have a dishwasher. Some would claim that washing dishes by hand will take less water and energy than loading them in the dishwasher and others would claim the opposite. So, which one is more efficient? Well, there is no straightforward answer to this question as it will depend on several factors such as your hand washing habits, your water fixtures, the use of warm or cold water, your dishwasher model and so on. We will look into all these factors to help you decide which method is best for you.
First let’s look at dishwashers, and see how they perform.
According to research, the average household in the UK does between 3 to 7 dishwasher loads a week. Your household may not fall within this threshold so we will make comparisons between washing one load in the dishwasher or by hand and then if you want to know your total weekly/monthly use, you can just multiply.
Ideally, a rating system from A+++ to D or A-G (like the one that exists for energy use) should be created for water use in dishwashers to make it clearer and more straightforward for consumers as a 2008 research paper points out. As this has not happened to date we will look at the information contained on the energy label for the best and worst performing models we can find online.
The water consumption of dishwashers is indicated at the bottom left-hand side of the label and is expressed in l/annum based on 280 standard cleaning cycles. Usually, you can also find the number of litres per cycle in the product information. Otherwise, you will have to divide the consumption in l/annum by 280 to find out how many litres of water per cycle a specific dishwasher uses.
This can help you identify the most water efficient dishwasher if you are only looking at products with the same capacity but it is not very helpful to compare products with different capacities. For example, when comparing a dishwasher that can hold 10 place settings with another that holds 12 place settings, the one with 12 place settings can use more water per cycle but will be washing more dishes so it could still be more efficient. You can verify that by dividing the number of litres per cycle or the annual water use by the number of place settings ( l/cycle/PS or l/annum/PS).
In my research, looking through different capacity dishwashers, I have found that the worst performing one available used approximately 1.3l/cycle/PS and the best 0.45l/cycle/PS; they had the same energy rating of A+. Let’s consider a 12 place settings dishwasher in the best case scenario and in the worst case scenario above.
To have an idea of how many items can fit inside of a dishwasher with that capacity let’s first establish what is meant by a place setting. A place setting consists of a dinner plate, a dessert plate, a single glass, a soup bowl, a tea cup with saucer and about 5 items of cutlery. Therefore, 12 place settings consist of around 132 items.
To wash these 132 items in the dishwasher you would use 5.4l in the best case scenario and 15.6l in the worst case scenario. That is between 40ml and 120ml per item.
If your dishwasher is old and does not have a label it will probably perform worse than the labelled ones; you should be able to find information in the product manual. The average 1970’s dishwasher uses up to 50l/cycle or 4.2l/cycle/PS or 380ml per item.
But what can be achieved by hand washing? Let’s see.
Analysing water use by hand washing dishes is a bit more complicated than looking at dishwashers as there will be great variation according to the habits of each person. We will look at three main scenarios and this should cover the majority of cases.
- Washing dishes while running the tap continuously
For this calculation, I will assume that it takes 5 seconds to scrub and rinse each item of cutlery and saucers, 10 seconds for all the other items and 2 seconds in between items (to put one item in the drying rack and pick up another). Therefore:
Cutlery: 5sx60 items= 300s
Saucers: 5sx12 items = 60s
Others: 10sx60 items = 600s
In between items 2sx129 = 258s
The above results in a total washing time of 20.3 minutes. Research would say that it would actually take approximately 60 minutes to wash all these items so I am being quite optimistic here. You can adjust the calculation above according to your own speed if you think you are faster or slower.
The amount of water you use in 20.3 minutes of running the tap will depend on the flow rate of your tap and how much you open it. The flow rate of a kitchen tap can range between 1.5l per minute to 50l per minute and above. A flow rate of 1.5lpm is too low and would not allow you to wash the dishes very effectively or take you more time to wash each item; anything above 5lpm would be very impractical as it would spill water everywhere; 4lpm is a comfortable flow for washing dishes effectively. So my assumption is that even if your tap has a higher flow you would only open it up to 4lpm. Therefore:
20.3minutes x 4lpm = 81.2l
Again you can edit the calculation above if you know your tap’s flow rate or you can just open your tap to the flow you normally use and see how many seconds it takes to fill a 1l jug and work it out (remember to drink this water or use it to water your plants later).
- Soaking dishes before washing
Some claim that soaking dishes before washing can save water, let’s have a look at that. For 132 crockery/cutlery items, you will need to fully fill the sink and still, they may not all fit inside it at once. You will probably just keep the water from the first load in the sink and then just place the items from the 2nd/3rd etc load inside the same water. A standard sink has an average 20 litres capacity, so lets assume this is the maximum amount of water you will use for soaking.
Then you will still have to scrub and rinse each item. Let’s assume you use no water during the scrubbing process as your dishes are already wet from the soaking and you will only use more water for rinsing. If it takes 2 seconds to rinse each item of cutlery and saucers and 4 seconds to rinse each of the other items with 2 seconds in between items:
Cutlery: 2sx60items = 120s
Saucers: 2sx12items = 24s
Others: 4sx60 items = 240s
In between items 2sx129 = 258s
The above results in a total water use time of 10.7 minutes which at 4 litres per minute equates to 42.8l. Adding this up to the 20l used for soaking you reach a total of 62.8 litres of water used. This is better than running the tap throughout, saving nearly 20l of water.
- Washing dishes without soaking/soaking while washing
This is the technique I use to wash my dishes. I start by plugging the sink drain and putting all my dishes in the sink. I then drop a quick 3 seconds splash of water on top of them while wetting my sponge on the running water. Next step, I turn off the tap and scrub all my cutlery with soap and move them to the smaller sink compartment.
Then I move on to the least dirty dishes and while I rinse them the water falls in the sink and soaks the dirtiest ones. I scrub several items in a row before rinsing and use no water during scrubbing as my sponge is constantly wet from rinsing the previous items. During the rinsing, water also falls over the cutlery with soap, reducing the time to rinse the cutlery altogether to around 10 seconds in the end. For this example I will consider 20s due to the amount of items and going back and forth from the draining board to place the items. Therefore the water use is as follows:
Initial splash: 3s
Cutlery rinse: 20s (for 60 items)
Saucers: 2sx12items = 24s
Others: 4sx60items = 240s
In between items = 2sx72items (remember we will rinse all the cutlery together) = 144s
The above results in a total water use time of 7.2 minutes which at 4 litres per minute equates to 28.8l.
As demonstrated by my little experiment above and by research, handwashing can never win unless you have a very old dishwasher. Research has also demonstrated that you would use more energy to heat the water when washing by hand than by using the dishwasher and that dishes come out generally cleaner from a new dishwasher then if they were done by hand.
If you also value your time you can stop feeling guilty about using your dishwasher (and about wanting to purchase one) and be sure that you are contributing to a reduction in water use (remember to fully load your dishwasher before using). If you don’t have a dishwasher and can’t have it for some reason I hope that my hand washing technique above can help you reduce your water use and Green It Yourself…Now!
Has this article been useful to you? Do you have a hand washing technique that uses even less water? Share with us below!