This depends on which Sodastream model you have.
Most of our sparkling water makers are only designed to carbonate water. However, in 2025 we launched the Sodastream MIX Soda Maker. This is our only soda maker that allows you to carbonate liquids other than water.
If you have a TERRA, E-TERRA, ART, DUO, ENSO or older machines, only water should be carbonated, otherwise you risk damaging your machine, not to mention making a big fizzy mess! The money-back guarantee and the warranty are both invalidated if you carbonate any liquid other than water in your sparkling water maker (except MIX). Fizz plain, cold water and add one of our flavours AFTER the water has been carbonated! You can of course re-fizz plain water that has gone flat in any of our sparkling water makers - just make sure the bottle is filled up to the water line with water.
You can read more about why the MIX allows you to fizz other liquids here.