The Tainted Hydro Phantasm is a Genshin Impact enemy that can mainly be found in Fontaine, but sometimes near the Oceanid boss; it drops the Drop of Tainted Water, Scoop of Tainted Water, and Newborn Tainted Hydro Phantasm, which are used as character and weapon Ascension materials.
There are very few Tainted Hydro Phantasms in Teyvat; if you're having trouble finding them, reference the maps below to help.
Where to Find Tainted Hydro Phantasm in Genshin Impact
Tainted Hydro Phantasms are generally few are far between, so if you encounter one by chance, I recommend defeating it to get a headstart on material farming. If you run out of these enemies in your World, you can go to a friend's World through Co-op and ask if you could farm there.
Court of Fontaine
Reference the image above for the locations of all Tainted Hydro Phantasms in the vicinity of the Court of Fontaine.
Beryl Region
Reference the image above for the locations of all Tainted Hydro Phantasms in the Beryl Region. They're fairly close to Teleport Waypoints, so farming in this area is comfortable.
Romaritime Harbor
Reference the image above for the locations of all Tainted Hydro Phantasms surrounding the Romaritime Harbor. You may need to use a Waverider to get to them.
Related: Fontaine Fishing Association Location, Items, & More! (Genshin Impact)
How to Defeat Tainted Hydro Phantasm in Genshin Impact
There are two types of Tainted Hydro Phantasms: Tainted Water-Splitting Phantasm and Tainted Water-Spouting Phantasm; each take on different shapes but have the same battle mechanics.
Tainted Hydro Phantasms are immune to Hydro, like many other enemies in Fontaine. I highly recommend always exploring with a DPS character that can React with Hydro to avoid immunity issues.
Additionally, Tainted Hydro Phantasms will enter an enraged state when you don't defeat them fast enough. In this state, they will become immune to Freeze, so a Cryo DPS isn't the best option against these floating bubbles, either. To easily defeat Tainted Hydro Phantasms, I recommend using a Dendro, Electro, or Pyro DPS.
To find more enemies in Fontaine, check out All Breacher Primus Locations in Genshin Impact here on Pro Game Guides.