Based on our research, the energy and water use for both is about equal. So, go ahead and wash those bags, but try to keep the water temperature low. And if you have a particularly dirty bag, filled with something sticky like peanut butter, it’s probably better to just throw it away. Better yet, use reusable containers instead!



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. Today, our question is from listener Jen Stevens. She cares a lot about her impact on the planet.

Jen Stevens: I haven't owned a car in over 10 years. I haven’t had any meat in over 20 years.

Megan Hall: One thing Jen does to reduce her impact is wash and re-use plastic Ziploc bags, but she’s wondering whether the heat and water she uses to clean the bags outweighs the benefit of re-using them. We have Alina Kulman and Molly Magid from our Possibly team to answer this question. Welcome, Alina and Molly.

Alina Kulman: Hi Megan!

Molly Magid: Hey!

Megan Hall: So what did you find out?

Alina Kulman: Well to figure this out, we visited Jen at home.

Molly Magid: Jen says, in general she avoids buying ziploc bags, but when she ends up with them, she washes and re-uses them as long as she can.

Alina Kulman: We wanted to find out how much heat and water Jen uses to wash a plastic sandwich bag, so we went to her sink to start our experiment. 

Molly Magid: First, we measured the temperature of the water- it was about 108 degrees. Then, put a pitcher beneath the faucet, to measure how much water she used to clean one bag. 

Jen Stevens: I turn it back inside out. Looks alright, I’d use that. 

Alina Kulman: To wash the bag, Jen used about four cups of water.  We did some calculations and found out that the oil burned to heat the water released about 11 grams of CO2.

Megan Hall: Ok, how does that compare to what it takes to make a new ziploc bag?

Molly Magid: We weren’t able to find those exact numbers, but we could calculate the emissions used to make and deliver the plastic in one bag. 

Alina Kulman: And based on those numbers, the production of a single sandwich bag uses about half a cup of water and releases about 5 grams of CO2.

Megan Hall:  That’s half the emissions and less water than washing a used bag!

Molly Magid: Not exactly, because these were rough calculations, the emissions and water used are probably about equal. 

Megan Hall: So should Jen keep washing and re-using her bags?

Molly Magid: Well, we do think it’s worth it, but only if she washes them with less water at a lower temperature. And if a bag is coated in something sticky, like peanut butter, it’s probably better to just throw it out. 

Alina Kulman: Or if a clean bag rips, she can recycle it by bringing it to a collection box- they’re near the entrance of most large stores.  

Megan Hall: Great, thanks for looking into this, Alina and Molly!  For more information or to ask a question about the way you recycle, use energy, or make any other choice that affects the planet, please use our question page.