## Common ground
Both options refer to devices that remove impurities from water, regardless of the method used.
## Options at a glance
**8419.40 – Electrical water purifiers**
- **Defining trait:** Uses electricity as the primary energy source for purification (e.g., via UV light or electrolysis).
- **Typical examples:** UV water purifiers, electric reverse osmosis systems.
- **Best fit when:** The device relies on electrical power to generate a purification effect (e.g., UV lamps, electrochemical reactions).
**8421.21 – Filtering or purifying machinery for water**
- **Defining trait:** Uses physical filtration, chemical treatment, or photochemical processes—not primarily electricity.
- **Typical examples:** Carbon filters, sand filters, ozone generators, solar-powered purification units.
- **Best fit when:** The core mechanism is mechanical filtering, chemical reaction, or light-based (non-electrical) purification.
## Key differences
| Feature | 8419.40 – Electrical | 8421.21 – Filtering/Purifying Machinery |
|--------------------------|-------------------------------|------------------------------------------|
| Primary energy source | Electricity | Not electricity-dependent |
| Core mechanism | Electrically powered process | Filtration, chemical, or photochemical |
| Example tech | UV lamps, electrolysis | Carbon filters, ozone, solar purification |
## How to choose
- Does it use electricity as the main method of purification (e.g., UV light, electrochemical reaction)? → 8419.40
- Is the main method physical filtration, chemical treatment, or non-electrical photochemical action? → 8421.21
## Overlaps & pitfalls
A device may use both electricity and filtration (e.g., a UV filter with a carbon pre-filter). In such cases, **choose based on the primary function**: if electricity drives the core purification step (like killing microbes), use 8419.40; if the main process is filtering or chemical treatment, use 8421.21. The wording does not specify priority—users should base selection on the device’s defining mechanism