An under-sink filter is enough when your water is already safe to drink and you want it to taste and smell better, or when a lab report names one problem that a dedicated cartridge handles: chlorine and chloramine, sediment, lead, fluoride, nitrate, arsenic or a low pH you would like raised. These systems connect to the cold line, feed a dedicated faucet or the main one, keep the minerals, waste no water and need no drain or tank, so they fit a small cabinet and install in about an hour.
Choose reverse osmosis instead when the report shows high total dissolved solids, salty or brackish water, several contaminants at once, or a level that a single cartridge cannot bring down far enough. An RO membrane removes most of what is dissolved in the water; it needs a drain connection and either a storage tank or a tankless pump unit. Our Under-Sink RO Systems collection covers those.
Within this collection, Crystal Quest offers one-problem units (fluoride, arsenic, nitrate, lead, alkaline) and the multi-stage Classic and SMART systems, Waterdrop adds ultrafiltration and direct-connect carbon systems, and the Brondell Coral is a compact three-stage unit with twist-in cartridges. Not sure which problem you have? Start with a Free Water Match.