Under-Sink RO Systems

Reverse osmosis inside the cabinet, with its own faucet at the sink. From compact tank systems to tankless units.

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Ordering from Rein Water

What to expect

  • Ships direct from the manufacturer

    Every order is packed and shipped by the brand that makes it. We submit your order to them within 2 business days.

  • Estimated delivery on product pages

    Brondell, Crystal Quest and Waterdrop product pages show a dated delivery window under the buy button before you order.

  • Returns by brand

    Each manufacturer sets its own return window and restocking fee. Check the terms for your brand before you order.

    Return terms by brand

  • Tracking as soon as it ships

    We email your tracking number within 1 business day of the shipment leaving the manufacturer.

How to choose an under-sink RO system

An under-sink RO system sits in the cabinet, connects to the cold line and the drain, and feeds its own faucet at the sink. The cabinet holds the filter housings, the membrane and, on tank systems, a small pressurized storage tank. This collection runs from compact 50 GPD tank systems to 1,600 GPD tankless units, with 1 to 17 stages.

Who it is for

Households that want treated water for drinking and cooking from one tap, with the equipment out of sight. Tank systems suit smaller budgets and lower daily use; tankless systems suit busy kitchens and tight cabinets.

What to compare

  • Capacity (GPD): the rated daily output. A family kitchen is usually well served in the middle of the range.
  • Tank or tankless: a tank keeps water ready but takes cabinet space; tankless filters on demand at a higher flow rate.
  • Stages: product pages list what each stage contains, from sediment and carbon pre-filters to the membrane and post-filter.
  • Faucet and fittings: most systems include a dedicated faucet; check the finish and whether your counter has a spare hole.
  • Replacement schedule: each product page lists the interval for its filters and membrane, and the Parts Store carries them by SKU.

Most systems here ship by parcel. A few larger units are quoted with delivery.

Common questions

Most are designed for DIY installation with a drain saddle and a dedicated faucet. A local plumber can fit one if you prefer. Our installer finder shows local plumbers and installers by ZIP code.

Each product page lists the replacement interval for its pre-filters, membrane and post-filter. Replacement filters are in the Parts Store by SKU.

Yes. The membrane sends reject water to the drain through a small line and a drain saddle fitted to the sink drain pipe.

PFAS reduction is claimed model by model. Several systems here list PFAS among the contaminants they reduce, and several are certified to NSF/ANSI 58. Check the reduction list and the certifications on each product page for the exact claim before you buy.

Systems in this collection currently range from about $140 to about $2,900 before shipping. Price follows daily output (GPD), the number of stages and tank or tankless design. Each product page shows the current price.