Seltzer water and club soda are both carbonated drinks, and club soda is a little bitter compared to seltzer water. It is also somewhat salty, as it contains a certain amount of sodium. When it goes through the transition of water to carbonation, it becomes effervescent water.
Club soda is milder than the majority of carbonated beverages out there. It is mostly used as a mixer in bars and clubs, hence the name, club soda. On the other hand, seltzer has more of a natural taste to it, and the most popular seltzers are those that are naturally carbonated.
Seltzer does not have extra salt or minerals. Seltzer is said to have a cleaner, fresher taste compared to club soda, and it is also said to be a healthier alternative to club soda, as seltzer does not contain many additives.