Under-sink filter or reverse osmosis: which do you have?
How to tell your system type in a minute, and which filters it takes.
A reverse osmosis (RO) system has a membrane and a small drain line. An under-sink filter that is not RO connects to the cold water line only, with no drain line.
The model label on the unit tells you for sure. Search it and we show the filters that fit.
How to tell in a minute
Open the cabinet under your sink and look at the unit.
- Reverse osmosis: a small tube runs from the unit to the sink drain pipe. Many RO systems also have their own small faucet on the sink. Some have a storage tank, and tankless ones are one box.
- Under-sink filter, not RO: one or more cartridges on the cold water line, with no tube to the drain.
Which filters each one takes
An RO system usually takes a set of filters: one or more filters before the membrane, the RO membrane, and often a filter after it. Many tankless systems use a few cartridges that click in from the front. An under-sink system that is not RO takes one or more cartridges of a set size.
Filters are not shared across every model, so match by the model of your system. On our product pages, "Fits these models" shows the systems Waterdrop lists for each filter.
Find the model on the label
Look on the side, back or front panel of the unit, like G3P600 or X12. The number printed on an old cartridge works too.