Argh I have this problem all the time--and being a city-dweller have no garage to use. I exchange mine at Zabar's, though, for not too much money! I think it's like $15? I'm sure there are other stores in the city that will do the same thing.

Our SF hardware store (Coles) has them and I wait to get their coupon in the mail before stocking up.

Contact your local homebrewing shop. They should be able to tell you where you can get your canister refilled. We've got a kegerator with beer (for hubby) and rootbeer (for kids) and my hubby gets the canister refilled all the time.

If you're in the Detroit or Ann Arbor, MI, area, check out Adventures in Homebrewing.

I think BBB has them and they have the $5 or 20% off coupon often.

Crate and Barrel sells the exchange refills ($14.95 each). Bed, Bath and Beyond sells the machines, so they must sell the exchange refills too.

Maybe Amazon carries them too?

I exchange at BBB with the 20% off coupon all the time and it ends up being about $12.

If you live in Brooklyn, WHISK in Williamsburg exchanges them for $15. It's a great deal.

Wait, you can use the BB&B 20% off coupon on the canister refills? That is life-altering info. I go through a canister every 3 weeks, so that's a decent amount of annual savings.

Here in B.C. Canada, I get them at London Drugs. They don't usually have coupons for them though. It's still cheaper than buying bottled fizzy though.

yes BBB takes the coupons. I use the $5 off $15 and get the canister for $10 at mine.

agreed with LisaHartjes,

Some more crafty homebrewers have old soda canisters (back when soda came in big tanks carbonated and not just syrup) and would be your best bet to ask for resources to get them refilled. But be warned, the places they send you will most likely be into a little more heavy duty things than filling a water bottle looking canister for you and you may get some chuckles when you go!

Just re-read my comment and saw it made little sense- I meant many homebrewers use old soda canisters for their beer that need carbonated once filled, so homebrew shops would be able to tell you local places that they send their brewers who need to pressurize their canisters.

most ACE hardware stores will also do it for $15. but i never thought to try BBB with the coupons! excellent idea.

I do the same as windycitypete. We purchased a big tank through a restaurant my husband works at with a siphon attachment and now we fill ours at home. Saves SO much money! We fill our main canister every few months and we drink around 20 bottles a day of carbonated water.

I did the same as windycitypete and hot tea. Per-liter refill cost is around 1.2 cents. A 20-pound tank costs around $18 to refill, and will do around 20-25 refills of Sodastream's 14.5 oz ("60 L") tank. Here's a blog entry I did about it, with some links to the suppliers:
http://www.meehawl.com/Blogfiles/2011/10/27/11/10/carbonation-cornucopiae/

I found a place in brooklyn that fills them for $5.00 and $10.00 on the spot. Its brooklyn Paintball and Amusment. . For me it was worth the trip and I didn't need to keep any large tanks around my children.

I always went to Basics Plus in the city... they have stores all over NYC, but I always went to the one on 45th & 2nd. They never run out of stock there & I think you can not get them anywhere cheaper. I now live in Brooklyn, and started to order them from their website (www.basicsplus.com). I think they don't deliver outside Manhattan, so I always get them delivered to my work now. I'm pretty happy with them.

You have to go to http://www.criticalpaintball.com/SodaMod-p/sodastream-sodamod.htm
and make sure you have a store anywhere around you who refills tanks (usually a paintball store is your best best). Once you get the SodaMod ($60) and the tank (the video link describes which tank is best for which machine) it's usually only $2-4 at a paintball store to fill :-)

Go Check out www.SodaCO2.com. They have multiple options for refilling your sodastream carbonator. They also have great recipes and tips! Awesome site for sodastream users.