Under-counter water filters — also called under-sink filters — are installed inside the kitchen cabinet beneath the sink, connecting directly to the cold water supply and feeding a dedicated filtered-water tap on the counter. Compared to tabletop dispensers, they keep the counter clear while providing continuous filtered water at the point of use.
In Hong Kong, under-counter filtration is commonly chosen for home kitchens, residential rentals, and small offices where a compact, unobtrusive setup is preferred over a standalone water dispenser. If you are still comparing options for the home, our home water filter buying guide walks through the main types.
What an Under-Counter System Provides
A piped-in under-counter filter connects to the mains cold water supply and sends filtered water to a dedicated tap — typically installed beside the main kitchen tap. The system runs continuously without manual refilling.
Depending on the filtration configuration, the output water is used for drinking directly from the tap, filling kettles or water bottles, food preparation, and brewing coffee or tea.
RO vs UF: The Core Decision
The choice between reverse osmosis (RO) and ultrafiltration (UF) is the main technical decision in any under-counter filter system. Both reduce bacteria and particles; the differences matter depending on your building’s water conditions and personal taste preference. For a deeper comparison of the two technologies, see our full RO vs UF guide.
RO (Reverse Osmosis)
Filters at 0.0001 microns. Designed to reduce dissolved heavy metals, bacteria, viruses, chlorine and most other contaminants, depending on water conditions, system design and maintenance. Also reduces dissolved minerals, producing a clean, neutral-tasting water. Requires a drainage connection — the filtration process produces some wastewater that drains away under the sink.
UF (Ultrafiltration)
Filters at 0.01 microns. Reduces bacteria, viruses and suspended particles, retaining natural minerals in the water. No drainage required. Water retains a more natural mineral taste.
How to choose:
- If your flat is in an older building, or you are uncertain about the condition of the building’s internal pipework, RO is generally the more cautious choice — it provides protection against dissolved heavy metals that UF cannot address.
- If your building’s plumbing is confirmed in good condition, UF is a simpler, equally reliable option.
- Taste preference is also a real factor: RO produces a purer, more neutral flavour; UF retains the natural mineral character of the water. There is no universal right answer — it depends on what you and your household prefer.
- Installation conditions matter: RO requires a drainage outlet under the sink. If your kitchen cabinet does not have a drainage connection available, UF avoids this requirement entirely.
Bio-Link can advise on the most appropriate configuration based on your building and kitchen conditions.
Bio-Link’s Under-Counter Solution
Bio-Link’s RO838 is an under-counter reverse-osmosis (RO) system designed for Hong Kong home kitchens and small offices. It connects directly to the cold water supply and delivers filtered water through a dedicated counter tap.
Key features:
- RO filtration with multi-stage filter cartridges
- Compact under-sink design
- SGS certified filtration system
- Suitable for residential kitchens and small commercial settings
- Bio-Link handles delivery and installation; on-site assessment recommended before ordering
Full specifications — dimensions, filter stages, daily output and tank capacity — are listed on the current product page.
Installation Requirements
Under-counter RO systems require the following at the installation point:
- Cold water inlet — accessible under-sink connection to the cold water supply
- Drainage — for RO systems, a drain connection is required for wastewater (typically the existing sink drain)
- Counter space for the output tap — a small hole drilled in the counter or sink deck for the filtered water tap
- Under-sink cabinet space — the filter unit and tank (if applicable) sit inside the cabinet; dimensions vary by model
UF under-counter systems do not require a drainage connection, simplifying installation in kitchens where the drain routing is awkward.
Bio-Link’s installation team handles all connection work. An on-site assessment before confirming the order is recommended to check cabinet space, plumbing access, and drain routing.
Filter Maintenance and Warranty
Under-counter filter cartridges require periodic replacement to maintain filtration performance. Replacement intervals vary by model, water usage, and local water quality.
Bio-Link proactively contacts clients to remind them of scheduled maintenance — you do not need to track filter replacement dates independently.
Maintenance and warranty
Maintenance and warranty for both the machine and the RO/filtration system are covered under Bio-Link’s ongoing maintenance plan. The specifics — including coverage period and what each service visit includes — are confirmed at the quotation stage, based on the system you choose and your installation conditions.
Frequently Asked Questions
What is the difference between an under-counter filter and a water dispenser?
An under-counter filter installs hidden inside the kitchen cabinet and outputs filtered water through a dedicated tap on the counter. A water dispenser (tabletop or freestanding) is a standalone unit placed on or beside a counter. Both provide continuous filtered water from the mains supply; the choice mainly comes down to counter space, aesthetics, and whether hot/cold output is needed (dispensers typically provide multiple temperatures; under-counter tap systems generally provide ambient or cold filtered water only).
Do I need RO or UF for my Hong Kong flat?
This depends on your building’s pipework condition and your taste preference. RO provides more comprehensive filtration including against dissolved heavy metals and produces a purer, more neutral taste — but requires a drainage connection. UF retains minerals, produces a more natural mineral taste, and has a simpler installation. For older buildings or where water pipe condition is unknown, RO is generally the more cautious choice. Bio-Link can advise based on your specific situation.
Does an under-counter RO system waste a lot of water?
RO systems produce some wastewater as part of the filtration process — this drains away under the sink. The ratio varies by system. If water efficiency is a concern, ask Bio-Link about the specific wastewater ratio for the model you are considering.
How often do filter cartridges need replacing?
Replacement intervals depend on the model, daily usage, and local water quality. Bio-Link will proactively remind you when replacement is due as part of the maintenance arrangement.
How are maintenance and warranty handled?
Maintenance and warranty for both the machine and the RO/filtration system are covered under Bio-Link’s ongoing maintenance plan. The specifics are confirmed at the quotation stage, based on the system you choose and your installation conditions.
Can an under-counter filter be installed in a rented flat?
Generally yes, as the installation only requires connecting to the existing under-sink plumbing and drilling a small hole for the output tap. Whether this is permitted depends on your tenancy agreement — check with your landlord before proceeding.
Contact Bio-Link
Bio-Link can recommend the most suitable under-counter configuration for your kitchen and building conditions.