Matters came to a head on Friday, when I tried to carbonate a bottle and it just sat there, fizzing and fizzing, without ever giving me the "stop" signal. I was also hearing a bit of a hissing sound, which made me wonder whether maybe the bottle wasn't screwed in securely, so I tried to readjust it—only to find that apparently there was still some pressure built up in the bottle, because the machine went off with a loud bang, spraying water everywhere and blowing off the bottom piece that Brian had already glued back in place once.
At this point, I came to the conclusion I probably should have reached before: it was time to refill the CO2 canister. I'd never actually done this before, and I was a bit nervous about it, because I'd heard one or two stories about sporting goods stores refusing to refill the Primo canisters on the grounds that their CO2 isn't "food grade." But as it turns out, the process went off with only one minor hitch (the Sports Authority store we tried first said its CO2 machine was broken, so we had to go to a nearby Dick's Sporting Goods). We just went in, said we had a canister to refill, paid at the front desk, took the canister to the back, and came back out with a full, cold canister. Once we put it back in the machine, voilà, everything was working once again.
So I now know that at the rate I go through seltzer, a single canister lasts me about 5 months. This means either that one canister doesn't carbonate nearly as many liters as the 200 claimed on the package, or else I drink a lot more seltzer than I realized. Based on the rate at which I've been topping up the bottle—about every other day—I think it must be a combination of the two. If I'm consuming seltzer at a rate of about 3.5 liters per week, then I got about 76 liters out of the first canister, and the refill cost me $4.27. So, assuming I get as many liters out of this second fill as I did the first time, which seems like a reasonable guess, that works out to about 5.6 cents per liter, not counting the negligible cost of the water. That's a savings of 34.4 cents per liter—or, if I continue to drink seltzer at the same rate, about $63 a year.
And, as an extra perk, there are no more seltzer bottles or cans in the recycling bin, which means we don't have to take it out as often.