Reverse osmosis
A semipermeable membrane with pores measured in fractions of a nanometer, pushed by house pressure. Water gets through. Dissolved solids, PFAS, lead, radiological contaminants and nitrate largely do not. It is the only residential technology that reliably handles the things carbon cannot touch — and it belongs on one tap, not on your whole house.
- Where
- Kitchen cold line
- Output
- 50–100 gpd
- Cartridges
- 6–12 months
- Membrane
- 2–5 years
- Installed
- $525–$1,100
- On site
- 2–3 hours
What an RO membrane actually takes out.
The short version: anything dissolved. Carbon works by adsorption and is excellent at organic chemistry and chlorine; a membrane works by exclusion, which is why it is the answer for the ionic and radiological contaminants carbon leaves behind.
| Contaminant | Typical reduction | Notes |
|---|---|---|
| PFAS | 95%+ | 95%+ reductionPublished studies generally put RO above 95% across the PFAS family, including the shorter-chain compounds where carbon performance falls off. EWG flags a PFAS-class compound in the ECUA system. |
| Lead | 97%+ | 97%+ reductionLead almost never comes from the plant — it is picked up between the main and your tap, from service lines, solder and brass fixtures. Which is exactly why the fix has to be at the tap. |
| Radium & alpha activity | 95%+ | 95%+ reductionThe contaminant group that put Pensacola at the top of the 2009 list. Naturally occurring in groundwater, and not removable by carbon. |
| Nitrate & nitrite | 90%+ | 90%+ reductionAgricultural and wastewater origin. Both were on the published detection list for this system. |
| Arsenic (V) | 95%+ | 95%+ reductionArsenic III needs an oxidizing pre-step to convert it before the membrane will hold it. Worth testing for if you are on a private well north of the ECUA boundary. |
| Total dissolved solids | 92%+ | 92%+ reductionThe number you can watch yourself with a $15 handheld meter. It is also how you know when the membrane is finished. |
| Chlorine & taste | 98%+ | 98%+ reductionHandled by the carbon stages ahead of the membrane, not the membrane itself — and the carbon is there to protect the membrane as much as to improve the taste. |
Each cartridge exists to protect the one after it.
Skip a prefilter change and you are not just drinking worse water — you are shortening the life of the most expensive component in the box.
- 01
Sediment prefilter · 5 micron
Catches rust, silt and the pipe scale that comes loose after ECUA works on a main. Cheap, and it is the reason the carbon behind it lasts.
- 02
Carbon block · chlorine and VOCs
Removes chlorine, chloramine and volatile organics. Critical: chlorine destroys thin-film composite membranes. This stage is a bodyguard first and a taste filter second.
- 03
TFC membrane · 50–100 gpd
The actual separation. Product water goes to the tank; the concentrate goes to drain through a flow restrictor sized to the membrane. Needs about 45 psi minimum to work properly.
- 04
Pressurized storage · 3–4 gallons
A membrane produces slowly. The bladder tank is what lets you fill a pot in twenty seconds instead of twenty minutes. Air charge should read 6–8 psi with the tank empty.
- 05
Post-carbon polish, optional remineralization
A final pass on the way to the faucet to strip any tank taste. If flat-tasting water bothers you, a remineralizing cartridge adds a few ppm of calcium and magnesium back and restores mouthfeel.
Where RO is the wrong purchase.
It will not soften your water. An RO under the sink treats maybe twenty gallons a week. Your shower glass, your dishwasher and your water heater never see it. If you have scale, you have a hardness problem and you need a softener.
It will not fix your shower. Chlorine dries skin and strips hair at the point it touches you. That is a point-of-entry problem, and carbon on the main is a quarter the cost of trying to solve it with membranes.
It does waste water. Conventional tank systems reject roughly three to four gallons for every gallon stored. For a normal household that is 60–120 gallons a month. A permeate pump cuts it meaningfully by recovering the back-pressure that otherwise fights the membrane as the tank fills.
Whole-house RO is almost never the right call. It makes sense above roughly 2,000 ppm TDS, on brackish coastal wells, or with unusual well chemistry. On ECUA water it is the classic overspend — a $4,000 mechanical room bought by somebody who wanted better coffee.
Installed price, not equipment price.
The spread is real. A cored hole in quartz, a long drain run, or a cabinet with no clearance under the disposal all move the number more than the equipment does.
Three-stage
$525–$695
Sediment, carbon, membrane. The right choice for a small household on an existing sink hole.
- Standard air-gap or non-air-gap faucet
- 3.2 gal bladder tank
- Cold feed tee and drain saddle
- First cartridge set
Five-stage + permeate pump
$795–$980
Our default. Adds a post-carbon polish and cuts drain water substantially on typical Pensacola pressure.
- Everything in three-stage
- Permeate pump — no electricity
- Post-carbon polish stage
- Inline TDS monitor
Five-stage + remineralization
$920–$1,100
For people who find demineralized water flat, or who are running an espresso machine off the line.
- Everything above
- Calcite / magnesium cartridge
- Refrigerator line tee if reachable
- Designer faucet options
Ongoing: roughly $70–$130 a year in cartridges, plus a membrane every two to five years at $60–$180. Cored hole in granite or quartz adds $85–$140. Refrigerator line runs longer than fifteen feet are quoted separately.
Not sure whether you need RO or carbon?
Most homes that call us about drinking water need one of the two, not both, and the numbers say which. Tell us what you have noticed and we will start there.