Reverse osmosis (RO) is a water filtration method that forces water under pressure through a very fine semipermeable membrane, which blocks dissolved solids, lead, fluoride and most contaminants while letting clean water through. It is the most thorough common home filtration, producing very clean water, but it works slowly and sends some water down the drain as waste. RO systems usually combine the membrane with carbon and sediment stages. This guide explains what reverse osmosis is and how it works.

Quick Answer

Reverse osmosis forces water through a fine membrane that blocks dissolved solids, lead, fluoride and most contaminants, producing very clean water. It is the most thorough common filtration, but it works slowly and wastes some water.

How Reverse Osmosis Works

Household water pressure pushes water against a semipermeable membrane with microscopic pores. Clean water passes through, while dissolved solids and contaminants are blocked and flushed away as wastewater. The result is very pure water. See how water filters work.

Key Takeaway: The membrane is the magic, and the cost. The fine RO membrane is what removes almost everything dissolved in the water, but pushing water through it is slow and leaves a concentrated stream that goes down the drain as waste.

What RO Removes

Reverse osmosis removes dissolved solids, lead, fluoride, nitrates and most contaminants, making it the most thorough common method. See what water filters remove and do filters remove fluoride.

The Trade-Offs

  • Slower flow: RO produces water slowly, usually into a storage tank.
  • Wastewater: it sends some water down the drain (tankless systems waste less).
  • Removes minerals: it strips beneficial minerals too; some systems remineralise.

Multi-Stage Systems

RO systems combine sediment and carbon pre-filters with the membrane, and sometimes a post-carbon or mineral stage. See best reverse osmosis systems and reverse osmosis vs carbon.

Is RO Right for You?

Choose RO if you want the most thorough filtration and can accept slower flow and some wastewater. For taste alone, a carbon filter is simpler. See how to choose a water filter.

FAQ

What is reverse osmosis?

It is a filtration method that forces water through a fine membrane, blocking dissolved solids, lead, fluoride and most contaminants while letting clean water through. It is the most thorough common method.

Is reverse osmosis water safe to drink?

Yes, RO water is very clean and safe. It removes minerals too, which some systems add back; many people drink RO water with no issue.

Does reverse osmosis waste water?

Yes, it sends some water down the drain as it concentrates contaminants, though tankless systems waste less. It is the trade-off for thorough filtration.

Bottom Line

Reverse osmosis forces water through a fine membrane that removes dissolved solids, lead, fluoride and most contaminants, making it the most thorough common filtration, with the trade-offs of slower flow and some wastewater. See our best reverse osmosis systems guide.

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