Megan Hall: Welcome to Possibly, where we take on huge problems like the future of our planet and break them down into small questions with unexpected answers. I’m Megan Hall. 

Today, we have a question from a listener:

Keith Munslow: My name is Keith Munslow, I'm a musician, and I’m from Providence.

Megan Hall: He and his wife drink a lot of seltzer.

Keith Munslow: I’d say we were buying like — for a week — five or six eight-packs of seltzer.

Megan Hall: But that still wasn’t enough for them.

Keith Munslow: We hated it being 10 o’clock at night and running out of seltzer and being like ‘Aw man!’

Megan Hall: But then he had an idea.

Keith Munslow: Wouldn’t it be great to never run out?

Megan Hall: Keith recently switched to making his own seltzer at home with a soda maker — a machine that makes sparkling water — and he wondered if using it was more energy efficient than buying seltzer by the can.

Megan Hall: We had Max Kozlov and Fatima Husain from our Possibly Team look into this question. Welcome, Max and Fatima! 

Max Kozlov: Hi, Megan! 

Fatima Husain: Hello! 

Megan Hall: So, before we talk about which method is better, will you explain in general how seltzer is made? 

Max Kozlov:  All seltzers, and carbonated beverages in general, are made by pumping carbon dioxide gas, or CO2, into a liquid, which makes the fizz.

Megan Hall: Is there a difference between a homemade seltzer and the kind I buy at the store?

Max Kozlov: To make seltzer at home, you fill your bottle with tap water, and then inject CO2 into that water using a special cartridge. 

Fatima Husain: When that cartridge is empty, it can be refilled with CO2 and used again. 

Max Kozlov: For store-bought seltzer, the carbonation is done at a factory, and the seltzer is shipped to stores. Then you might drive there to pick them up.  

Megan Hall: So, is there really a difference in terms of greenhouse gas emissions for soda you make at home versus soda from the store?

Fatima Husain: Well, not in terms of making the actual soda. But remember, seltzer from the store comes in cans and bottles. And a lot of energy goes into not only making them, but also transporting the weight of all that liquid.

Max Kozlov: Which creates a lot of greenhouse gas emissions. 

Fatima Husain: Soda maker machines, on the other hand, just use your tap water at home, a reusable bottle, and a CO2 cartridge.  

Megan Hall: How often do you replace those cartridges?

Max Kozlov: Not as often as you open a new can of soda. Each SodaStream cartridge can carbonate about 60 liters of water, which is equal to about one-hundred-and-seventy 12-ounce cans.

Megan Hall: Wow, that’s a big difference. But you said making soda releases CO2. Should we be worried about that getting into the atmosphere? 

Max Kozlov: Carbon dioxide is a major greenhouse gas, but let’s put it into perspective.

Fatima Husain: One study between the Carbon Trust and Coca Cola UK found that the total carbon emissions for a can of Coke was about a third of a pound of CO2 — most of which came from the packaging, which you’d avoid with a seltzer maker at home.

Max Kozlov: By comparison, the average car releases that much CO2 after driving less than half a mile — Keith probably drives farther than that just to buy his seltzer.

Megan Hall: So what would you tell Keith?

Fatima Husain: Homemade seltzer is responsible for fewer carbon emissions than store-bought seltzer. 

Megan Hall: Does that mean I should rush out and buy a soda maker?

Max Kozlov: Not necessarily. If you drink a LOT of seltzer, like Keith, it might be a good idea. 

Fatima Husain: But, soda isn’t high on the list of the things that lead to climate change.

Max Kozlov: So, if you’re worried about your greenhouse gas emissions, start with taking fewer trips in your car or eating less meat.

Megan Hall: Great! Thanks, Max and Fatima!

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, go to the public’s radio dot org slash possibly. Or subscribe to us wherever you get your podcasts. 

Possibly is a co-production of the Institute at Brown for Environment and Society, Brown’s Climate Solutions Initiative, and the Public’s Radio.