das Soda
soda water
Water with carbon dioxide added, also called soda water. It is often drunk plain or used as an ingredient in mixed drinks.
Ich hätte gern einen Whisky mit Soda.
I'd like a whisky with soda water.

soda water / soda / heartburn
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soda water
Water with carbon dioxide added, also called soda water. It is often drunk plain or used as an ingredient in mixed drinks.
Ich hätte gern einen Whisky mit Soda.
I'd like a whisky with soda water.

The German 'Soda' (soda water, m01) is usually just carbonated water. It is not the same as the English 'soda', which often refers to sweet soft drinks like Coke or Fanta.
Bestell in einer deutschen Bar ein „Soda“, wenn du Sprudelwasser möchtest.
Order a 'Soda' (soda water) in a German bar if you want sparkling water.
You can recognize the meaning of 'Soda' (soda water/soda/heartburn) from context. In a bar, it means soda water (m01). In connection with chemistry or cleaning, it refers to the chemical (m02). If someone complains about physical discomfort after eating, it means heartburn (m03).
Für den Cocktail brauche ich noch einen Schuss Soda.
I still need a splash of soda water for the cocktail.
The use of 'Soda' (heartburn) for 'Sodbrennen' (heartburn) is colloquial. It is especially common in Austria and parts of Bavaria.
Hast du etwas gegen Soda? Mir ist ganz schlecht.
Do you have anything for heartburn? I feel really sick.
When referring to the drink, 'Soda' (soda water) is often used in fixed combinations, for example 'ein Schuss Soda' (a splash of soda water), 'mit Soda aufgießen' (to top up with soda water), or in names of mixed drinks such as 'Wodka Soda' (vodka soda).
Viele Leute trinken im Sommer einfach nur Soda mit einem Stück Zitrone.
In summer, many people just drink soda water with a piece of lemon.
mineral water
'das Mineralwasser' and 'das Soda' can both refer to water for drinking. 'Mineralwasser' comes from a protected spring and contains natural minerals. It can be sparkling or still. 'Soda' here means carbonated water, often as soda water for mixed drinks. Learners may confuse the words because both occur in restaurants or when shopping. If the origin and the minerals are important, you say 'Mineralwasser'; if it is mainly about sparkling water for mixing, 'Soda' fits.

Für den Saft mischt sie etwas Soda dazu, damit das Getränk frischer schmeckt.
She mixes a little soda water into the juice so that the drink tastes fresher.
Im Supermarkt kauft meine Nachbarin stilles Mineralwasser für das Abendessen.
At the supermarket, my neighbor buys still mineral water for dinner.