Reverse Osmosis: Definition & Professional Guide
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Reverse osmosis is a water purification process that forces water under pressure through a semipermeable membrane with pores approximately 0.0001 microns in diameter, blocking dissolved salts, heavy metals, bacteria, viruses, and organic compounds while allowing purified water molecules to pass through. Reverse osmosis systems remove up to 99 percent of dissolved contaminants, making them the most effective residential water purification technology available for point-of-use drinking water.
Semipermeable Membrane, Pre-Filters & Waste Concentrate Ratio
Natural osmosis moves water from a region of low solute concentration to high solute concentration through a membrane, seeking equilibrium. Reverse osmosis applies external pressure (typically 40 to 80 psi from residential water supply) to force water in the opposite direction, from the concentrated (contaminated) side through the membrane to the dilute (purified) side. The contaminants rejected by the membrane are flushed to a drain line as waste concentrate.
The RO membrane is the core component, but residential systems include multiple pre-treatment and post-treatment stages. A sediment pre-filter removes particles that would foul the membrane. An activated carbon pre-filter removes chlorine, which degrades thin-film composite (TFC) membranes. After the membrane, a post-carbon filter removes any residual taste or odor. Some systems add a remineralization stage that reintroduces calcium and magnesium for improved taste and alkalinity.
Residential RO systems produce purified water slowly, typically 50 to 100 gallons per day, storing it in a pressurized tank for on-demand use through a dedicated faucet. The process generates wastewater at a ratio of approximately 3 gallons of waste per 1 gallon of purified water in standard systems, though high-efficiency models reduce this to 1:1 or better.
Under-Sink, Countertop, Whole-House, Tankless & Commercial RO Types
Under-sink RO systems are the most common residential configuration, installed beneath the kitchen sink with a dedicated dispensing faucet. They typically include 4 to 6 filtration stages and a 3 to 4 gallon pressurized storage tank.
Countertop RO systems require no permanent installation and connect to the faucet with a diverter valve. They are suitable for renters or as temporary solutions.
Whole-house RO systems treat all water entering the home, providing purified water to every fixture. They require large storage tanks, repressurization pumps, and higher-capacity membranes. These systems are used primarily on well water with high total dissolved solids.
Tankless RO systems eliminate the storage tank by using a high-output membrane and booster pump to deliver purified water on demand. They produce water at a higher flow rate and take up less under-sink space than tank-based systems.
Commercial RO systems are scaled-up versions used in restaurants, medical facilities, and industrial applications. They use multiple membrane housings in parallel for higher production capacity.
RO Installation, Water Quality Testing & Membrane Replacement Services
RO system installation requires plumbing connections to the cold water supply, a drain connection for wastewater, and installation of a dedicated dispensing faucet, typically requiring a new countertop penetration. Bonded Plumbworks’ water filtration services include RO system selection, professional installation, and annual membrane and filter replacement.
In areas where municipal water contains chloramine disinfectants and naturally high dissolved minerals, RO systems significantly improve drinking water quality. Bonded Plumbworks helps homeowners select appropriately sized systems based on household water consumption and incoming water quality test results.
NSF/ANSI 58, EPA Safe Drinking Water Act & State Code Certification
NSF/ANSI 58 is the certification standard for reverse osmosis systems, defining contaminant reduction claims and performance testing protocols. The State building codes require that RO systems installed on potable water lines carry NSF 58 certification. The EPA’s Safe Drinking Water Act establishes the Maximum Contaminant Levels that RO systems are designed to meet or exceed.
APEC, iSpring, Waterdrop, Pentair & Culligan RO Systems
APEC produces the ROES-50 and Ultimate series residential RO systems. iSpring manufactures multi-stage RO systems with UV post-treatment options. Waterdrop offers tankless RO systems with high-efficiency membranes. Pentair produces the GRO and FreshPoint RO lines. Culligan provides professionally installed RO systems with ongoing service contracts.