If there is any-what makes seltzer water different from club soda from tonic water?
Aren’t they all just carbonated water?
Tonic water contains quinine. I figure all the G&Ts I drink will ward off the malaria.
Club soda is just fizzy water.
Not really. Tonic water contains quinine. In general use, I would say that seltzer water is freshly carbonated water, using a cartridge, club soda is carbonated and bottles, and tonic has the aforementioned added ingredient. YMMV.
Wrong. Check the packaging. Club soda has sodium. Seltzer water is fizzy water with natural flavors. I have a can of seltzer right in front of me.
Quick googling reveals that it “may” contain sodium bicarbonate, depending on bottler. However, I haven’t any packaging, as I don’t often have occasion to use it.
Wikipedia thinks that Seltzer is typically pure fizzy water, while Club Soda may have small amounts of “…table salt, sodium citrate, sodium bicarbonate, potassium bicarbonate, potassium sulfate or disodium phosphate, depending on the bottler.”
In my experience, the salt or whatever takes some of the edge off the CO2. Still, if you are using the carbonated water as a mixer, the additional ingredients probably don’t matter.
Tonic water, OTOH, has a distinctive taste.
Tonic water is sweetened. Is has approximately as many calories as Coke or Sprite. That makes it entirely unlike seltzer and club soda.
And flavored (and not just with quinine. You can buy tonic water without quinine.)
So you’d have to drink at least 24 litres a day to treat malaria. Good to know! 
Tonic water is a flavor, like cola, root beer, or orange.
To me club soda and selter are pretty much interchangable, ususally one has salt one doesn’t, but both serve as a base for adding flavors to make ‘soda’s’ - though they can be drunk straight.
I have both in my house. 
I can go through a case of seltzer in a hot weekend, so I make sure there is no sodium.
the club soda works better for mixed drinks because of the pinch of salt.
It is my impression that tonic water has less sugar than soda pop.
Some googling shows that we are both right: apparently there are varieties with 4, 10 and 114 calories. (Coke has about 110 calories, IIRC).
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114: Calories in Tonic Water | CalorieKing
The first is probably diet tonic water (which you can find alongside the regular at the grocery store.) The point is that tonic water is closer to soda than to carbonated water; some people who posted above implied that the difference between carbonated water and tonic water was the presence of quinine, which is not really correct.
What Excalibre said, pretty much. Your first link is to “slimline” or “Indian” diet tonic water. Your second has the wrong quantity. The link should instead be: 1 can or bottle (12 fl oz) Tonic Water, which gives a calorie count of 124.
To be fair to those people, around these parts (and pretty much everywhere I’ve ever traveled, outside bits of the East Coast) I have never seen tonic water refer to anything but quinine water. I’d be a bit surprised if I ordered a gin and tonic and it had a different flavor in it.
Thanks for telling me about club soda. I have always lived on the right-hand side of the Atlantic and never knew what this drink was. I have only ever heard of it - until now - in old movies where some craggily handsome guy orders it in a bar and is commisirated (“on the wagon, huh?”). I had speculated that it was a movie euphamism for Coke/Pepsi in the days before the maturity of product placement.