This article explains the treatment objective, the design information that matters and the operating checks that help keep the system practical after installation.
What an under-sink system is
An under-sink purifier is installed in the cabinet below a kitchen sink, connected to a dedicated tap (or sometimes the existing tap via a diverter) so that only the water used for drinking and cooking passes through the purification stages — commonly sediment filtration, carbon filtration and often RO, depending on what the source water requires. This differs from a whole-house system in that it treats a single point of use rather than every fixture in the property, and differs from a benchtop/countertop unit mainly in that it is installed out of sight below the counter rather than sitting on top of it.
When an under-sink system is a sensible fit
Under-sink systems are commonly chosen where the household's main water-quality concern is specifically drinking and cooking water, rather than water used for bathing, laundry or general household use — this is the majority case for most Bangladesh households, since arsenic, high TDS, hardness and similar dissolved-solids concerns primarily matter for water that is consumed rather than water used for washing.
Storage tank versus tankless (direct-flow) designs
Some under-sink RO systems include a small pressurised storage tank (holding a reserve of treated water so it is available on demand without waiting for the membrane to produce it in real time), while newer tankless designs produce filtered water on demand without a storage tank, generally taking up less cabinet space but sometimes with a different flow-rate characteristic. Which is more appropriate depends on the household's typical usage pattern and available cabinet space, not a universal preference for one design over the other.
Installation and space considerations
Under-sink systems need adequate cabinet space, a nearby drain connection for RO reject water (where RO is included), and in most cases a dedicated small tap installed through the countertop or sink deck — these are practical installation details worth confirming before committing to a specific unit's dimensions, particularly in smaller kitchens common in many Dhaka apartments.
Matching the system to the actual source water
As with any residential water-treatment decision, what stages an under-sink system actually needs (sediment only, carbon, RO, or a combination) should be based on the household's specific water test results rather than a generic assumption — a WASA-supplied kitchen with generally acceptable TDS has quite different requirements from a tube-well-supplied kitchen dealing with iron, hardness or arsenic.
Need a treatment recommendation for your water?
Send the water source, intended use, approximate demand and any available test report. Waterwise Bangladesh can review the requirement and discuss an appropriate treatment approach.
