REVERSE OSMOSIS FACTS
Reverse osmosis is the most thorough drinking water filter you can install at a kitchen sink. A certified system reduces dissolved substances like nitrate, lead, arsenic, fluoride and many PFAS that carbon filters can’t touch. It isn’t magic, though. Here’s what RO does, what it doesn’t, and how to tell a certified system from a marketing claim.
Last updated October 2026
How Reverse Osmosis Works
An under-sink RO system cleans water in stages before it reaches its own faucet.
1. Sediment filter
Catches sand, rust and grit that would clog the system.
2. Carbon filter
Removes chlorine, taste and odor, and protects the membrane, which chlorine can damage.
3. RO membrane
Water is pushed through a membrane with extremely fine pores. Dissolved substances are held back and rinsed to the drain.
4. Polish or remineralize
A final filter polishes taste. Some systems add back calcium and magnesium for a smoother, less flat taste.
What Reverse Osmosis Reduces
Every home RO system certified to NSF/ANSI 58 must prove it reduces total dissolved solids (TDS). Beyond that, manufacturers can earn optional claims for specific contaminants. These are the ones most relevant to Iowa homes:
Commonly certified reductions
Nitrate and nitrite
Lead
Arsenic (pentavalent)
Fluoride
Barium
Copper
Hexavalent and trivalent chromium
Radium 226/228
Selenium
Cysts like Giardia and Cryptosporidium
Total dissolved solids (minerals, salts)
What RO doesn’t handle alone
Bacteria and viruses: RO is not a disinfection system. Well water must test bacteria-safe first or be disinfected.
Trivalent arsenic: RO alone doesn’t reduce it enough to earn a certification claim.
Whole-home water: RO treats drinking water at one faucet, not showers or laundry.
Hardness throughout the house: that’s a water softener’s job.
A system’s certification only covers the contaminants listed on its performance data sheet. Always match that list to your water test results.
Does Reverse Osmosis Remove PFAS?
Reverse osmosis is one of the most effective home treatments for PFAS, the “forever chemicals.” EPA researchers report that high-pressure membranes like RO typically remove more than 90% of a wide range of PFAS, including shorter-chain types.
The catch: not every RO system is certified for PFAS. The EPA recommends looking for a system certified to NSF/ANSI 53 or 58 specifically for PFAS reduction. If PFAS is your main concern, ask us which systems carry that claim.
Does Reverse Osmosis Remove Nitrates?
Yes. Nitrate/nitrite reduction is one of the standard optional claims under NSF/ANSI 58, and it’s the main reason many Central Iowa families install RO. Boiling and carbon pitchers don’t reduce nitrate at all.
How Much Water Does Reverse Osmosis Waste?
Every RO system sends some water down the drain to rinse away what the membrane rejects. Older tank-style systems often send about 3 gallons to the drain for every gallon of drinking water. Many newer tankless systems flip that ratio, producing 2 to 3 gallons of drinking water for every gallon sent to the drain.
Since you’re only treating water for drinking and cooking, the total is small compared to a shower or a load of laundry. Look for the efficiency or recovery rating on the system’s performance data sheet; NSF/ANSI 58 sets how those are tested.
A typical older tank system
1 gallon to the faucet • 3 gallons to the drain
Tank vs. Tankless Reverse Osmosis
We install both. Here’s how they compare under your sink.
Feature
Tank system
Tankless system
Storage tank
Yes, about the size of a basketball
No, water is filtered on demand
Cabinet space
Takes more room
Frees up most of the cabinet
Power needed
No
Yes. Needs an outlet that isn’t on a wall switch
Water to drain
More (often about 3:1)
Less (often 1:2 or 1:3)
Flow at the faucet
Slows as the tank empties
Steady
Display
No
Shows filter life and water quality on the unit
Systems we install
iSpring RCC7-AK alkaline
Safe Water Iowa SWI 600B+, Waterdrop G3P600 and G3P800
Does RO Remove Healthy Minerals?
Yes. RO removes calcium and magnesium along with everything else dissolved, which is why some people find plain RO water tastes flat. Remineralization fixes that by adding a small amount of minerals back after the membrane.
The Safe Water Iowa SWI 600B+ has remineralization built into one of its filter stages. The iSpring RCC7-AK adds an alkaline remineralization stage. Other systems can add a separate remineralization filter.
RO also reduces fluoride. If you rely on tap water fluoride for your family’s dental health, ask your dentist whether to supplement.
Can RO Water Go to My Refrigerator?
Yes. We can run a line from your RO system to your refrigerator’s water and ice dispenser, so the same filtered water comes out of the fridge door. Tell us about your fridge when you request an estimate.
Reverse Osmosis Questions From Iowa Homeowners
Is reverse osmosis worth it on city water?
For many Des Moines-area families, yes. City water meets federal standards, but RO adds another layer for nitrate, PFAS and lead, and most people notice a big taste difference. It also replaces buying bottled water.
Is reverse osmosis good for well water?
It can be part of the plan, but test first. RO doesn’t disinfect, so a well must be bacteria-safe or have disinfection like UV before RO goes in.
How long does installation take?
Most under-sink installs take about 2 hours.
How often do filters need changing?
Pre-filters are typically changed every 6 to 12 months and the membrane every 2 to 4 years, depending on your water and use.
What does NSF/ANSI 58 certification mean?
It’s the national standard for home reverse osmosis systems. A certified system has been independently tested for its claims and confirmed not to add anything harmful to your water.
We’ll look at your water, your sink and your goals, then recommend a certified system with a clear, upfront estimate.
Why Iowa homeowners choose reverse osmosis
Sources
NSF/ANSI 58 overview (NSF)
EPA: Identifying Drinking Water Filters Certified to Reduce PFAS
EPA WaterSense RO specification
Water Conditioning & Purification: NSF/ANSI 58 contaminant testing