What Does a Reverse Osmosis (RO) Water Filtration System Actually Do?

What Does a Reverse Osmosis (RO) Water Filtration System Actually Do?

Reverse osmosis is a water treatment process that uses pressure to force water through a semi-permeable membrane. This membrane allows water molecules to pass through while rejecting many dissolved salts, metals and other impurities.

In simple terms:

  • Tap water is pressurised
  • Water passes through a fine membrane
  • Many dissolved substances are left behind and flushed away

This process is widely used in:

  • Drinking water treatment
  • Food and beverage production
  • Medical and laboratory applications
  • Desalination of seawater

How a Typical RO System Works

Most household reverse osmosis systems use multiple stages:

  1. Pre-filtration
    Removes sediment, rust, and chlorine to protect the RO membrane.
  2. Reverse Osmosis Membrane
    The core component that reduces dissolved solids, salts, and many contaminants.
  3. Post-filtration (Carbon polishing)
    Improves taste and removes any residual odours before water is dispensed.
  4. Storage Tank
    RO filtration is slow, so filtered water is stored for on-demand use.

Some systems may also include additional stages such as remineralisation or UV treatment, depending on design.

What Does Reverse Osmosis Remove?

Reverse osmosis is particularly effective at reducing:

  • Microplastics
  • Total dissolved solids (TDS)
  • Salts and minerals (sodium, calcium, magnesium)
  • Heavy metals (such as lead, arsenic, mercury)
  • Fluoride (depending on membrane and system design)
  • Nitrates and sulphates

The exact reduction performance depends on the membrane specification and system maintenance.

Source:
NSF International – Reverse Osmosis Drinking Water Systems
https://www.nsf.org/consumer-resources/water-quality/water-filters-testing-treatment/reverse-osmosis

What RO Systems Do Not Automatically Do

While RO is highly effective, it’s important to understand its limitations:

  • It does not disinfect water unless paired with UV or similar treatment
  • It removes many naturally occurring minerals along with contaminants
  • Performance declines if filters and membranes are not replaced on schedule
  • It produces some wastewater as part of the filtration process

RO systems are designed for chemical and dissolved contaminant reduction, not as a standalone microbiological treatment in unsafe water supplies.

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