A Missed Pop-ortunity: With their promise of convenience and inexpensive soda, can home soda makers deliver the goods?

Whether you're interested in making a refreshing glass of classic seltzer or plan to venture where no soft-drink mixologist has gone before—Diet rhubarb cola, anyone? How about a refreshing kiwi-mango spritzer?—one of these soda makers or seltzer siphons might be just the tool you need. Besides the fun factor and opportunity to concoct newfangled flavors, the gadgets bear a modicum of "green": Because they utilize reusable glass, metal, or plastic bottles, they reduce the amount of waste you produce. Finally, manufacturers claim the gadgets can pump out carbonated beverages for mere pennies a liter. We set out to determine if soda makers and seltzer siphons are really worth it.

How They Work
Soda makers use compressed carbon dioxide (CO2) gas to charge still water—no batteries or electricity required. There are two types of devices:

Multiuse soda makers are tall, plastic-bodied countertop appliances that resemble old-fashioned milkshake mixers; they take up approximately the space of a small coffeemaker. The units conceal refillable, screw-in CO2 cylinders that can carbonate dozens of servings before requiring replacement. (The cylinders range in size from a can of whipped cream to a small kitchen fire extinguisher.) To charge water, you add plain water to the device's mixing bottle, screw the bottle onto the machine, press the button (or lever) to release a dose of CO2, and—voilà!—sparkling H2O. (One model, the Right Choice Drinkit, can dispense soda by the glass or into a container placed under its spout.)

Single-use soda siphons are basically a metal-bodied version of the seltzer bottle a circus clown might wield. They rely on smaller single-use disposable CO2 cartridges that screw into the siphon head and charge the water held in the siphon bottle. The entire soda siphon is stored in the refrigerator.

Most manufacturers also sell flavoring syrups, including old stand-bys like cola and lemon-lime and exotics like kiwi and sarsaparilla, which you add to the water after carbonation. You can also buy brand-name syrups like Coke and Pepsi from retail outlets.

How We Tested
We used the Mr. Butler's Italia Fizzy Drinkmaker, Right Choice Drinkit, Soda Club Edition I, and Soda Club Penguin to make cola, diet cola, lemon-lime, and diet lemon-lime sodas according to the manufacturers' instructions. We also made plain seltzer with both the soda makers and the soda siphons. We tasted all of the beverages immediately after charging. Although the soda makers allow you to adjust the level of carbonation, we did not supercharge any of the beverages to create an "atomic soda," fearing injury to life, limb, and our sensitive palates. We capped and refrigerated a second batch of beverages for 10 days. After that time, we tested them to see how the carbonation kept. Additionally, we had a few children test-drive the Soda Club Penguin; indeed, they were more interested in making the soda than in drinking it.

What We Found
When used with name-brand flavoring syrups, all of the soda makers produced pop that tasted very much like the real thing. One exception was the Mr. Butler "Diet Coke" flavor, which testers deemed "watery." Also noteworthy were Soda Club's regular flavors, which contain only one-third of the sugar of conventional sodas. Some tasters, however, characterized the Soda Club flavors as having an unpleasant "artificial" taste, likely due to the presence of the artificial sweetener Splenda.

The soda makers also carbonated beverages well, at least in part because you can control the amount of carbonation. Soda siphons, which have only a fixed amount of CO2 at their disposal, fared less well, with fizz ranging from low (iSi) to high (Liss, after the recommended 1-hour refrigeration). Surprisingly, all of the "homemade" beverages that we stored for 10 days retained their carbonation as well as or even better than store-bought controls, which were opened and then also tested after 10 days.

The Bottom Line
Factoring out the initial cost of the devices, all of the soda makers and siphons produced serviceable seltzer and soda for less money than the nationwide average ready-made soda price of 80 cents per liter. But unless you're a gadgethead or enjoy funky flavors, stick with the store-bought stuff. That way you'll never have to worry about mixing syrups or having enough CO2 on hand. Heck, you might even win whatever prize is hidden under the twist-off cap.