When choosing an under-sink water purifier, there are several parameters to consider:

1. **Type of Water Purifier:**
– There are several types available including Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF), and Reverse Osmosis (RO). When selecting, consider the filtration technology, filter effectiveness, ease of cartridge replacement, lifespan, and replacement cost.

2. **Microfiltration (MF):**
– Filtration precision typically ranges from 0.1 to 50 microns. Common types include PP filter cartridges, activated carbon filter cartridges, and ceramic filter cartridges. Used for coarse filtration, removing large particles such as sediment and rust.

– Disadvantages include inability to remove harmful substances like bacteria, inability to clean filter cartridges (often disposable), and frequent replacement required.

3. **Ultrafiltration (UF):**
– Filtration precision ranges from 0.001 to 0.1 microns. Utilizes pressure difference membrane separation technology to remove rust, sediment, colloids, bacteria, and large organic molecules.

– Advantages include high water recovery rate, easy cleaning and backwashing, long lifespan, and low operating cost.

4. **Nanofiltration (NF):**
– Filtration precision is between UF and RO. Requires electricity and pressure for membrane separation technology. Can remove calcium and magnesium ions but may not completely remove some harmful ions.

– Disadvantages include low water recovery rate and inability to filter certain harmful substances.

5. **Reverse Osmosis (RO):**
– Highest filtration precision of about 0.0001 microns. Can filter almost all impurities including bacteria, viruses, heavy metals, and antibiotics.

– Advantages include high desalination rate, high mechanical strength, long lifespan, and tolerance to chemical and biological influences.

In terms of filtration capability, the ranking is typically Microfiltration > Ultrafiltration > Nanofiltration > Reverse Osmosis. Both Ultrafiltration and Reverse Osmosis are suitable choices depending on preferences. Ultrafiltration is convenient and low-cost but cannot be consumed directly. Reverse Osmosis is convenient for high water quality needs, such as for making tea or coffee, but may require additional steps for consumption. It’s recommended to choose according to your specific requirements and preferences.