Reverse osmosis water systems for Los Angeles County.

Pressure forces water through a membrane that blocks dissolved solids at the molecular level.

Reverse osmosis uses household water pressure to push tap water across a semipermeable thin-film composite membrane with pores small enough to block dissolved ions, molecules, and microscopic particles. Contaminants that do not pass through are flushed to drain. Purified water collects in a pressurized storage tank and is delivered through a dedicated faucet at the kitchen sink.

The membrane works by size exclusion and ionic charge rejection. Water molecules (H2O) at 0.28 nanometers pass through. Chromium-6 ions, arsenic ions, nitrate ions, PFAS molecules, and dissolved salts are all significantly larger and are rejected at rates of 85 to 99 percent depending on the contaminant and feedwater conditions.

For Los Angeles County water specifically, the high chloramine content (LADWP uses chloramines as the primary disinfectant rather than free chlorine) requires two activated carbon pre-filter stages instead of one, because chloramines break down more slowly than free chlorine. The five-stage systems we install are sized for this water profile.

• 1
  Sediment pre-filter

  Removes silt, rust, and suspended particles down to 5 microns. Protects the carbon stages and the membrane from premature fouling.

• 2
  Carbon block pre-filter

  Removes chlorine, chloramines, and organic compounds. Chlorine degrades RO membranes, so this stage is critical for municipal water.

• 3
  Second carbon block

  A second activated carbon stage for chloramine-heavy supplies such as LADWP, which uses chloramines as the primary disinfectant.

• 4
  RO membrane

  The core stage. A thin-film composite membrane rejects dissolved solids, chromium-6, arsenic, nitrates, PFAS, and most other ionic contaminants at the molecular level.

• 5
  Remineralizing post-carbon

  Adds calcium and magnesium back into purified water, improving taste and replacing beneficial minerals removed by the membrane.

What NSF 58 certification actually guarantees.

NSF/ANSI Standard 58, developed by NSF International and ratified by the American National Standards Institute, is the governing certification for residential point-of-use reverse osmosis drinking water systems sold in the United States. Certification under this standard requires independent laboratory testing at an NSF-accredited facility, not self-reporting by the manufacturer.

The standard covers three areas. First, contaminant reduction: the system must achieve the claimed reduction percentage for each contaminant listed on the certification at the concentration specified in the standard. Second, structural integrity: the system housing and connections must withstand pressure testing without leaking. Third, material safety: all wetted components must not introduce new contaminants into the treated water above threshold levels.

For Los Angeles County homeowners evaluating a reverse osmosis system, the practical check is to look for the NSF 58 certification mark on the product and verify the specific contaminants listed in the NSF Certified Drinking Water Treatment Units database at nsf.org. Chromium-6 and PFAS reduction must be listed explicitly. Not all NSF 58-certified systems are certified for every contaminant within the standard's scope.

All reverse osmosis systems we install carry NSF 58 certification covering the specific contaminants documented in Los Angeles County, Orange County, and San Diego County water supplies. We provide the certification documentation at installation.