Reverse Osmosis Systems

Reverse osmosis (RO) systems use a semi-permeable membrane to remove up to 99% of dissolved contaminants. Available as under-sink (tank or tankless) and countertop models.

Written by WaterFilterMatch Editorial TeamOctober 2026

System Cost

$190 - $2,000

Annual Filters

$75 - $340 in replacement filters

Installation

DIY moderate to advanced

How It Works

Water passes through pre-filters (sediment + carbon) to protect the RO membrane, then is forced through the membrane at high pressure. The membrane has pores of roughly 0.0001 microns - small enough to reject dissolved salts, heavy metals, fluoride, and most organic molecules. Rejected water (concentrate) goes down the drain. A post-carbon filter polishes taste. Tank-based systems store 3-4 gallons of filtered water; tankless systems filter on demand at 0.4+ GPM.

What It Removes

Removes Well

TDS and dissolved minerals (95-99%)
Lead, arsenic, chromium, and heavy metals
Fluoride (93-98%)
PFAS/PFOA/PFOS
Nitrates and radium
Bacteria and viruses (most models)
Microplastics

Does NOT Remove

Chlorine gas (removed by pre-filters, not the membrane)
Some dissolved gases
Beneficial minerals (removed along with contaminants - some models add remineralization)

Installation

DIY moderate to advanced. Under-sink models require connecting to the cold water supply and drain. Most need a dedicated faucet hole drilled in the countertop; tankless models (Waterdrop G3/D6/X series) also need an outlet under the sink. Countertop RO (AquaTru, Waterdrop K19 and M6H) requires no installation - just plug in and pour.

Who Should Choose Reverse Osmosis Systems?

Good fit if you...

✓Well water or high-TDS municipal water
✓Anyone needing fluoride removal
✓Households with lead, arsenic, or PFAS contamination
✓Families who want the broadest possible contaminant removal
✓Immunocompromised individuals (RO removes bacteria and viruses)

Not ideal if you...

✗Homes with very low water pressure (below 40 PSI without a booster)
✗People who dislike the taste of demineralized water (get a model with remineralization)
✗Eco-conscious buyers bothered by water waste (tankless models run 2:1-3:1 pure-to-drain vs 1:3-1:4 for older tank systems)
✗Budget-constrained buyers - upfront and ongoing costs are highest