Riddle me this...

Tonic water is full of sugar, even though it's bitter tasting. Club soda is just carbonated water and mineral water is carbonated mineral water. I don't know what seltzer is. Your best bet would be the sparkling mineral water.

I loooove sparkling mineral water as an alternative to sodas. Whole Foods sells an Italian sparkling mineral water (naturally sparking at the source - no carbonation added). It's 365 brand and 99 cents for a 1-liter bottle. I've compared it to the brand names (Gerolsteiner, etc.) and can't tell the difference.

I don't know what the others are specifically, but know that their not as natural. Also, beware some of the flavored waters out there. Many of them contain splenda or aspartame as sweeteners. MIL thought she was doing me a huge favor buying them for me when I was pregnant. Till I pointed out the ingredients list . . .

I buy sparkling mineral water. Trader Joe's sells Blu Italy for under a $1 a bottle.

Club soda has ... sodium bicarbonate? ... added to it. Some kinda sodium anyway.

Yes, club soda is "sparkling water" with SALT added (good for cocktails, not so good for regular drinking). Seltzer is plain old sparkling water, just with much more carbonation than sparkling mineral water. As someone who has tried the "soda transition" before, I think seltzer is your best choice in terms of retaining the "bubbly" feeling of diet soda--sparkling mineral water is much less fizzy.

We are huge seltzer fans here! We also buy Knudsen Spritzers too. Usually when they are on sale we stock up. They have sparkling water and real natural flavors. Of course, we could make our own spritzers too, but no one can agree on a flavor.

When I was pregnant with Ayla I was really attracted to the fizziness of soda also, but even the organic seltzers and sodas are often filled with sugar (albeit organic sugar). So, what I did, and it's still a favourite... was to buy something like San Pellegrino and mix it with organic fruit juices or a fresh-squeezed citrus fruit. It was sooo good, I still drink it all the time. It gives you the satisfaction of pop but without the bad stuff. Definitely go for the mineral water though... it's actual water.

We like the Crystal Gyser fruity flavored sparkling water. We get them at TJ's . I also like Calistogas.