It doesn't have salt in it i don't think! Ewww imagine drinking salt water! Here are the ingredients from a web site:
Soda water or club soda, seltzer water, carbonated water
Water which has been charged with carbon dioxide to produce a carbonated beverage. It also contains sodium bicarbonate which can be soothing on an upset stomach. Soda water is used as the basis of some soft drinks and mixers.
I can't see that it has anything bad in it (although i'm not an expert or a CDC) so i'll carry on drinking it - hasn't affected me so far!
Sodium bicarbonate is the chemical compound with the formula NaHCO3. Because it has long been known and is widely used, the salt has many other names including sodium hydrogencarbonate, sodium bicarb, baking soda, bread soda, cooking soda, bicarb soda or bicarbonate of soda. The word saleratus, from Latinsal æratus meaning "aerated salt", was widely used in the 19th century for both sodium bicarbonate and potassium bicarbonate. The term has now fallen out of common usage.
It is soluble in water. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slight alkaline taste resembling that of sodium carbonate. It is a component of the mineral natron and is found dissolved in many mineral springs. The natural mineral form is known as nahcolite. It is also produced artificially.
Main article: Solvay process
NaHCO3 is mainly prepared by the Solvay process, which is the reaction of sodium chloride, ammonia, and carbon dioxide in water. It is produced on the scale of about 100,000 ton/year (year: 2001).
Commercial quantities of baking soda are also produced by this method: soda ash, mined in the form of the ore trona, is dissolved in water and treated with carbon dioxide. Sodium bicarbonate precipitates as a solid from this method:
Na2CO3 + CO2 + H2O → 2 NaHCO3