A reverse osmosis system sits under the kitchen sink and runs water through several stages before it reaches a small faucet on the counter. For a Provo household, it is one way to get drinking and cooking water with fewer dissolved minerals and certain contaminants. It does have tradeoffs: it sends some water down the drain, needs regular filter changes and only reduces what it is certified to reduce. Here is how it works and what to check first.
How a Reverse Osmosis System Works, Stage by Stage
The EPA WaterSense page on point-of-use RO systems explains the core idea. In reverse osmosis, pressure forces water through a semi-permeable membrane. Water passes through, and most dissolved material is held back. That splits the supply into two streams: treated water, called permeate, and reject water, called concentrate or brine. The concentrate carries rejected minerals to the drain and keeps the membrane surface rinsed.
Household water pressure does the pushing, and each stage protects the next.
- Sediment pre-filter: a fine cartridge catches sand, silt and rust flakes that would clog the membrane.
- Carbon pre-filter: activated carbon adsorbs chlorine and many taste and odor compounds. Chlorine can damage many thin-film membranes, so this stage guards the membrane.
- RO membrane: a tightly wound sheet inside a pressure housing, where dissolved solids are separated out.
- Post filter: a final carbon cartridge, often called a polishing filter, treats water on its way from the tank to the faucet.
What Reverse Osmosis Removes, and Why to Test First
Removal claims are only as good as the testing behind them. The NSF/ANSI 58 standard for reverse osmosis systems requires every certified system to show total dissolved solids (TDS) reduction. Other claims are optional, and each one is tested separately. They include lead, copper, arsenic, fluoride, nitrate and nitrite, radium, cysts and volatile organic compounds.
The WaterSense guide to selecting water treatment systems advises checking the performance data sheet for your target contaminants. It also notes that RO does not remove every contaminant, and that it removes minerals such as calcium along with them.
So start with your water. EPA requires community water systems to send an annual Consumer Confidence Report by July 1, so this year's report should be out by mid-August. It lists your water source and the regulated contaminants detected. For results from your own tap, the WaterSense guide points to a state-certified lab.
Wastewater, the Storage Tank and the Faucet
RO is slow, so the system makes water ahead of time and stores it. A small pressurized tank holds the treated water, and an air charge inside pushes it to the faucet. When the tank fills, an automatic shutoff valve stops production. A check valve keeps stored water from flowing back toward the membrane.
The concentrate leaves through a flow restrictor and a drain saddle clamped to the sink drain above the P-trap. EPA WaterSense says a typical point-of-use system sends five gallons or more down the drain for every gallon of treated water. Labeled models must stay at 2.3 gallons or less. Actual ratios vary by model and water conditions. Utah State University Extension also lists heavy water use among the drawbacks of RO.
The dedicated faucet mounts on the sink deck, sometimes as an air gap faucet.
Pairing Reverse Osmosis With a Water Softener
A softener and an RO unit solve different problems. The USGS guide to water hardness explains that hardness comes from dissolved calcium and magnesium, which can leave scale in pipes and water heaters. A softener treats all the water entering the house, trading those minerals for sodium through ion exchange.
That helps the RO system too. As water passes through the membrane, hardness minerals concentrate on the reject side and can form scale on the membrane surface. Softened feed water lowers that load. The WaterSense guide lists sodium among what RO removes, so the RO faucet also reduces the sodium a softener adds to drinking water.
Our water softener service covers whole-house softening, and both systems can be planned so the RO feed comes after the softener.
Why Output Drops and What You Can Check Safely
Most RO problems trace back to pressure or buildup. A loaded pre-filter acts like a partly closed valve, so less pressure reaches the membrane and production slows. Hard water can scale the membrane, and chlorine that slips past a spent carbon stage can wear it down. A worn membrane lets more dissolved solids through. A tank that has lost its air charge holds less water, so the faucet runs out sooner.
The WaterSense guide says to replace filters on the manufacturer's schedule, since unmaintained systems may make water quality worse. Pre-filters usually come due before the membrane. WaterSense criteria require a labeled system's membrane to last at least one year.
- Filter dates: compare the service label on each housing with the manual.
- Faucet flow: time how long a glass takes to fill when the tank is full.
- Drain sound: nonstop trickling at the sink drain with a full tank can point to a faulty shutoff valve.
- TDS reading: a handheld meter shows whether treated water reads higher than before.
A Provo Scenario You Might Recognize
Picture a family in Provo whose RO faucet has slowed to a thin stream during a hot August stretch, when everyone drinks more water. The storage tank empties after a few glasses and takes hours to recover. The pre-filters have not been changed since the system went in. The home has hard water and no softener, and their TDS meter reads higher than it once did.
That pattern points to more than one worn stage. Loaded pre-filters starve the membrane of pressure, so production drops. The higher TDS reading suggests the membrane is scaled or worn. A technician would still check the tank air charge and the shutoff valve first, since both can cause similar symptoms.
Safety Notes
- Shut off the feed first: close the RO supply valve and open the RO faucet to release pressure before opening any housing.
- Expect water: set a towel and a shallow pan under the unit first.
- Use the right wrench: snug housings by hand or with the housing wrench. Overtightening can crack a housing or pinch its O-ring.
- Leave the air gap alone: it helps keep drain water from backing up into the system, so do not remove or bypass it.
- Watch for drips: check every fitting for a day after service. The EPA guide to mold and moisture says drying wet materials within 24 to 48 hours helps prevent mold growth.
- Sanitize as directed: if the manual calls for sanitizing housings during a filter change, use only the product it names.
When to Call a Professional
Changing pre-filters is routine upkeep for many owners. Call a professional when the job touches your supply or drain piping, or when the cause is unclear.
- New installation: tapping the cold supply, mounting the faucet and connecting the drain saddle all change your plumbing.
- Leaks that return: a drip after reseating a fitting may mean a cracked housing or worn tubing.
- Nonstop drain flow: a failed shutoff or check valve wastes water around the clock.
- Confusing test results: a report full of numbers is easier to act on with help.
Towers Plumbing serves homes across our Provo service area. Our water filtration service can help you read your water report and compare treatment options for the kitchen tap.
Frequently Asked Questions
Does reverse osmosis remove hardness?
It reduces calcium and magnesium, which are dissolved solids. But a point-of-use unit treats only one tap, and hard water can scale its membrane over time. A softener handles hardness for the whole house, including the water heater.
Is a certified RO system certified for every contaminant?
No. NSF/ANSI 58 requires only a TDS reduction claim. Check the performance data sheet for each contaminant you care about, such as lead, arsenic or nitrate.
Does an under-sink system treat the whole house?
No. It serves only one tap. The WaterSense guide says whole-house systems suit water sources with consistent, significant contamination, and it suggests treating only the water used for drinking and cooking.
Plan Your Reverse Osmosis System With Towers Plumbing
Before you reach out, gather a few details. Find this year's water quality report or any lab results, and note the hardness and TDS numbers if listed. Note whether the home has a softener, and check under the kitchen sink for a cold supply valve and room for a tank. For an existing system, write down its age and the last filter change. Note any symptoms, such as slow flow or a drain that never stops.
Then contact Towers Plumbing through our contact page and share those notes, along with a photo of the space under the sink. A technician can review your water, explain which stages fit your goals and walk you through the options before any work begins.