What Is Reverse Osmosis and How Does It Work?
Reverse osmosis (RO) is a water purification process where pressure forces water across a semipermeable membrane that blocks heavy metals, chemicals, and almost anything else but the water molecules from passing through. Purified water flows to your faucet on-demand, while the rejected impurities are rinsed down the drain.
Why This Matters for You
RO’s unique process addresses many water quality issues that other filtration methods often can’t. The combination of pressure and a semipermeable membrane helps remove up to 99% of lead, arsenic, pesticides, and other harmful contaminants, as well as high levels of total dissolved solids (TDS) that can alter your water’s taste, odor, and clarity. So, if your local water quality isn’t great even after standard home or municipal treatment, a reverse osmosis water filter is worth considering.
How it works, step-by-step
STEP 1
Sediment & carbon come first
Before water ever reaches the membrane, it passes through a sediment filter that catches grit and a carbon filter that removes chlorine or chloramine. This is protective housekeeping – chlorine and sharp particles would shorten the membrane’s life.
STEP 2
Water is forced against the membrane
Normal osmosis would pull water toward the more concentrated side. Reverse osmosis flips that: applied pressure drives water the “wrong” way – from the contaminated side toward the clean side – overcoming the natural pull.
STEP 3
Water passes; contaminants don’t
The membrane’s pores are around 0.0001 microns – small enough that water molecules squeeze through while dissolved salts, heavy metals, and most other contaminants are turned away. The filtered stream is called permeate.
STEP 4
A final carbon pass, then to your tap
Filtered water often rests in a small storage tank, then runs through a final polishing carbon filter on its way to the faucet – a last step for crisp taste. Meanwhile, the concentrated leftovers are continuously rinsed to the drain.
Reverse Osmosis for Well Water vs. City Water
|
Key Considerations |
Well Water |
City (Municipal) Water |
|---|---|---|
|
Typical targets |
Nitrates, arsenic, pesticides, some heavy metals, high TDS |
PFAS, disinfection byproducts, residual chemicals, trace metals, chlorine taste/odor |
|
Prefiltration needs |
Sediment and iron/sulfur treatment, softening for hard water, and chlorination or UV purification for certain microbes |
The RO unit’s built-in sediment and carbon prefilters may suffice. |
|
Membrane lifespan |
Shorter lifespan without proper pretreatment; the membrane can foul, scale, or clog faster and need earlier replacement. |
Typically longer life with treated city feed water and timely prefilter changes. |
|
Testing expectations |
Highly recommended due to the lack of federal regulation and monitoring of private wells. The homeowner is responsible for regular well testing. |
Water quality reports are helpful, but water tests are often more accurate. |
What This Means for Maintenance
Many RO systems employ multiple filters that can wear out or become saturated with particulates over time. Replacing these filters on time enhances the system’s filtration performance, extends its lifespan, and ensures your water is always at its freshest. Here’s a general schedule to follow:
PRE-FILTERS
Replace Prefilters Every 6-12 Months
Sediment and carbon prefilters gradually clog up with contaminants, which can restrict or stop water flow, damage components, and reduce your water quality. Replacing these first-stage filters on schedule helps prevent these outcomes.
post / polishing filter
Change Post/Polishing Filter Every 12 Months
A fresh carbon postfilter keeps your water tasting crisp and clean and prevents chemical-like, stale, or “tank” flavors, so be sure to replace it at least once a year.
MEMBRANE
Replace RO Membrane Every 2-3 Years
The RO membrane’s thin and highly porous material makes it more susceptible to clogging, chemical damage, and bacterial growth. Swap it out as recommended for purer, fresher water.
Discover the Benefits of Reverse Osmosis Water at Home
Reverse osmosis filtration provides almost complete assurance that your home’s water is free of harmful contaminants and unpleasant tastes and odors. That way, you can hydrate, cook, prepare beverages, and more with confidence and peace of mind. Check out SpringWell’s Moen Under-Sink Reverse Osmosis Filtration System today to see if it’s the right fit for your home.