The answer is a resounding NO. Based on our experiment, handwashing used 5 times more water and about 4 times more energy than a modern dishwasher. And according to our research, older dishwashers still have better water and energy use than hand washing. You can save even more water and energy if you don’t pre-rinse your dishes and just scrape off any food scraps
Megan Hall: Welcome to Possibly, where we take on huge problems like the future of our planet and use science to find everyday solutions.
I’m Megan Hall. In the US, one out of five households don’t use a dishwasher because they think it uses more water and energy than washing by hand. So, we wanted to test this out: is hand washing really more efficient than using a dishwasher?
Alina Kulman and Molly Magid from our Possibly team put this question to the test. Welcome Alina and Molly.
Alina Kulman: Hi Megan!
Molly Magid: Hello!
Megan Hall: So, what did you find out?
Alina Kulman: Well, we went to Molly’s house since she has a dishwasher.
Molly Magid: I told my roommates to stop washing their dishes for a few days, so we had a stack of dirty dishes ready.
Alina Kulman: We put a five-gallon bucket beneath the faucet and measured the temperature of the warm water. Molly got ready to wash the dishes.
Molly Magid: We’ve got a new sponge for this! (washing noises)
Alina Kulman: …you now have a bucket full of soapy, dirty water.
Molly Magid: After the first bucket filled up, I dumped the water and started washing again.
Alina Kulman: I mean it’s just crazy to see fully how much water you’re actually using because I use probably a similar amount.
Molly Magid: Yeah usually the water just goes down the drain and you don’t have to think about the total amount you’re using.
Megan Hall: Ok so how much water did you end up using to wash the dishes?
Alina Kulman: Molly used three full buckets which totaled fifteen gallons of water
Molly Magid: Based on the temperature of the water, we were able to calculate that heating it with gas released about 900g of CO2.
Megan Hall: How does that compare to the water and energy used by the dishwasher?
Molly Magid: Well, I have a newer dishwasher made by Bosch. And according to the company’s calculations, a typical wash cycle uses about 1 gallon of water and releases about 260g of CO2.
Alina Kulman: That means that when we hand washed the dishes, we used 15 times more water and about 4 times more energy than the dishwasher!
Megan Hall: Wow! So everyone should just use their dishwasher?
Molly Magid: According to our research, older dishwashers still have better water and energy use than hand washing. And you can save even more if you don’t pre-rinse your dishes and just scrape off any food scraps.
Alina Kulman: But if you don’t have a dishwasher or you’re washing a set of fancy china by hand, you can fill a bin in the sink with hot soapy water.
Molly Magid: That’ll use less water and energy because the faucet isn’t constantly running, and you only have to change the water when it gets dirty.
Megan Hall: Great! Thanks Alina and Molly.
That’s it for today. For more information or to ask a question about the way you recycle, use energy, or make any other choice that affects the planet, visit our question page.
Possibly is a co-production of the Institute at Brown for Environment and Society and the Public’s Radio.
Check our work!
These are the calculations we did for this episode
Hand Washing:
Water used = 15 gallons
Temperature of water = 100° Fahrenheit
Temp Change = 100-65 = 35° Fahrenheit
Q(heat) = 35*56781.18*4.184 = 8,315,036 J= 8,315 KJ of heat = 2.309 KWh
For RI electricity: 870.8 lbs/MWh = 0.394988236 kg/KWh (from: http://bit.ly/2kGu5t0)
Amount of CO2 released: 0.394988236 * 2.309 = 0.912317 kg CO2 = 912.3 g CO2
Bosch Dishwasher:
Uses 1 gal/wash and 0.67 KWH/wash, (from: http://bit.ly/2m1yB5j)
Water used = 1 gallon
For RI electricity: 870.8 lbs/MWh = 0.394988236 kg/KWh (from: http://bit.ly/2kGu5t0)
Amount of CO2 released: 0.67 KWH * 0.394988236 kg/KWh = 264.6 g CO2