The real difference is your daily routine.
Reverse osmosis (RO) water filters use a membrane system to separate part of the incoming water from a reject stream. Whether the appliance is under your sink or on the counter determines how you install, fill and maintain it.
Choose countertop RO if…
- You rent or cannot modify the existing sink setup.
- You have spare worktop area and a safe power outlet.
- You do not mind topping up a tank and handling the reject-water compartment.
- You may want an appliance with instant hot-water functions.
Choose under-sink RO if…
- You have room inside the cabinet and can fit an additional faucet.
- Suitable feed-water, drainage and electricity are available.
- You prefer getting filtered water directly at a tap rather than refilling a reservoir.
Trade-offs nobody should skip
Countertop systems can take significant space and need daily handling. Under-sink systems require more planning and fitting, and remain dependent on ongoing filters. Both have electricity and reject-water considerations, which depend on the actual model and usage.
Three concrete examples
G3P600 is an under-sink option; M6SL is a countertop option without hot dispensing; M6HG adds hot dispensing.
Sources & verification
Facts below are taken from the linked sources; product information may change. Last editorial check: 13 November 2026. No hands-on product testing was performed.