Reverse Osmosis Explained: How an RO System Actually Works

A reverse osmosis system is the most thorough drinking water treatment you can put under a residential sink. It works by pushing water through a semi-permeable membrane with pores small enough to block dissolved solids that ordinary carbon filters pass straight through.

Stage by stage

• Sediment pre-filter: catches sand, silt and rust so the membrane is not blinded early
• Carbon pre-filter: strips chlorine and chloramine, which would otherwise damage the membrane
• RO membrane: the actual separation stage, rejecting the majority of dissolved solids
• Storage tank: holds treated water because the membrane produces slowly
• Carbon post-filter (polish): removes any tank taste on the way to the faucet
• Optional remineralization: adds back a small amount of calcium and magnesium for taste

What RO reduces

Depending on membrane rating and water conditions, RO substantially reduces total dissolved solids, lead, arsenic, nitrates, fluoride, sodium, and many other dissolved contaminants. Look for systems whose components are tested to NSF/ANSI 58 for the specific claims that matter to you.

The wastewater question

RO membranes flush rejected solids to drain, so some water is sent down the line for every gallon produced. Older systems were inefficient. Modern permeate-pump and high-efficiency designs cut that ratio dramatically, and the total volume is still small next to what a shower or irrigation cycle uses.

RO and hard water

This matters in San Antonio: hardness fouls RO membranes fast. Installing RO downstream of a softener extends membrane life significantly. If you are considering both, install them together and size them as one system rather than bolting RO onto hard water later.

Does RO water taste flat?

Some people find very low-TDS water flat because minerals contribute to taste. A remineralization cartridge adds a controlled amount of calcium and magnesium back after the membrane. It is inexpensive and easy to add at install.

BlueWell Water Co tests hardness, chlorine and TDS at your kitchen sink for free anywhere in the San Antonio area, then quotes only the equipment your house actually needs.