The only dedicated tap on our kegerator is the one for carbonated water. All beverages are marked up when you buy them by the serving rather than in bulk, but carbon dioxide dissolved in water is one of the most egregious. Making 5 gallons at home costs less than a dollar. When it comes to bottles, smaller is better because after opening the bubbles begin to escape. Having it on tap ensures the water is always ideally carbonated, and wonderfully cold (especially compared to our 75F/24C summertime tap water).Seltzer, sparkling water, fizzy water, and bubbly water are synonyms, referring to water with carbon dioxide bubbles. In the US, "mineral" water is required to have 250 parts per million total dissolved solids (TDS), usually from a natural spring. Club soda or soda water is similar, but usually has the minerals added to it. Adding quinine (from cinchona tree bark) would turn it into tonic water. I don't think there is any need to get technical when making your own.
Luckily the process to carbonated water at home couldn't be simpler, if you already have a kegerator. Fill a keg with good tasting water (e.g., carbon-filtered tap water, reverse osmosis) and connect to a CO2 tank. Set your regulator for between 20-30 PSI, depending on how strong you want the bubbles to be. Once the keg is connected vent the head-space and then let the water chill and the CO2 infuse. To speed things up, once the water is chilled, you can shake the keg to speed up the absorption of the gas. Cold water can hold onto CO2 much easier, so you're wasting your time to shake room temperature water.
We add a small dose of chalk (calcium carbonate) to move our tap water closer to the profile of Perrier. Chalk doesn't readily dissolve at water's roughly neutral pH, but it is happy to once there is carbonic acid in solution. This is essentially the same thing that happens with acid rain meets limestone, the carbonic acid dissolved in the rain eats away at the calcium carbonate in the rock.
My Treated Water
Calcium
|
Chloride
|
Sulfate
|
Sodium
|
Magnesium
|
Carbonate
|
150
|
30
|
50
|
15
|
10
|
250
|
Perrier
Calcium
|
Chloride
|
Sulfate
|
Sodium
|
Magnesium
|
Carbonate
|
160
|
19
|
30
|
9.6
|
4.3
|
366
|
The calculator on this site includes many more profiles if you have a favorite mineral water.
If you are a fan of flavored seltzers like Polar or La Croix, you could add a small dose of a natural flavoring of your choice. It is best to dose a glass to taste and then scale up, a little goes a long way when it comes to these super-concentrated "natural" flavorings like those from Amoretti. You can also use actual natural ingredients like citrus peel. In that case I'd remove those after hanging them in the keg for a day or two. If you stick with plain water there is no need to clean or sanitize between fills, but with strong flavors you may need to clean if you are switching flavors.
This post is also available in video form on my YouTube channel.