Reverse osmosis has earned a reputation as one of the most powerful tools we have for cleaning up drinking water. Properly designed systems can remove the vast majority of dissolved salts, heavy metals, pesticides, and even microplastics, whether you are running a small under-sink unit at home or a high-capacity skid in a hospital or food plant. Yet in practice, water quality at the tap is never just about the membrane. The materials you choose for pipes, tanks, housings, and fittings quietly shape how pure, safe, and stable that water remains as it moves through the system.
As a hydration specialist, I see the same pattern over and over. A facility or homeowner invests in a good membrane but then couples it with the wrong metals, plastics, or tank materials. Over time, the “polished” water starts picking up metals, plastic additives, or off-flavors from the very infrastructure meant to deliver it. On the flip side, the right materials can keep low-mineral, aggressive RO water stable for years, simplify cleaning, and reduce microplastic and chemical exposure.
In this deep dive, we will look at what the research says about the major materials used in commercial and residential RO systems, how they behave with low-mineral water, and how to make practical, health-focused choices without over-specifying or overspending.
Why RO Water Is Hard on Materials
Reverse osmosis is essentially a demineralization process. Water is pushed under pressure through a semi‑permeable membrane that passes water molecules while rejecting most dissolved salts, organics, and microorganisms. Guidance from Puretec and other engineering sources describes modern RO systems routinely removing about 95–99% of dissolved contaminants when they are properly designed and maintained.
That high level of purification creates a less obvious side effect: the finished water can become more aggressive toward many materials. Stainless steel tank manufacturers note that RO water is demineralized and therefore more corrosive toward traditional mild steel or concrete tanks. Without the buffering of dissolved minerals, water is more likely to dissolve metals or additives from surfaces it touches, especially over long storage times.
The effect gets even stronger in RO/DI systems, where RO is followed by deionization resin. The American Society of Plumbing Engineers (ASPE) highlights that RO/DI water is “mineral-starved” and will aggressively leach metals and plastic additives if the wrong materials are used. In hospital applications, this has real consequences for both water purity and device longevity. The same chemistry applies in a home kitchen, even though the stakes and volumes are smaller.
In short, once you strip the minerals out, water starts looking for something else to dissolve. Material choice is one of your main tools to keep that “something else” from being your plumbing, storage tank, or faucet.
The Heart of the System: Membrane Materials
Thin-Film Composite Polyamide: The Workhorse
Across both commercial and residential systems, the standard RO element today is a thin‑film composite polyamide membrane. Articles from Puretec and Cannon Water Technology describe these as multi-layer structures: a very thin, dense polyamide “skin” on top of a porous support. That thin skin does the separation work, screening out most salts, many organic molecules, and microorganisms while allowing water to pass.
These membranes operate at microscopic scales. Bevi cites a study in which RO membranes with extremely fine pores were able to remove about 99.9% of microplastics and nanoplastics from tap water. The pores are small enough that, in Bevi’s description, they can block particles hundreds of thousands of times smaller than a human hair. Multiple sources, including Just Plumbing AZ and Aquatech Water Systems, echo that properly maintained RO systems routinely reach microplastic removal rates in the 99.9% range in test conditions.
The same polyamide chemistry that makes these membranes so effective also has implications for materials and maintenance. A review in Water Science & Technology and a study in Chemosphere, summarized by Bevi, point out that polymer-based membranes themselves can become a source of microplastics as they age, foul, or mechanically degrade. Under prolonged use, tiny fragments can shed from the membrane surface.
That does not negate the benefits of RO. The available evidence indicates that RO still removes far more microplastics than it introduces. But from a materials perspective, it reinforces two points. First, pretreatment and maintenance matter because fouled or chemically attacked membranes degrade faster. Second, downstream materials—including post-filters and piping—can either trap any shed particles or simply act as another pathway for plastics to enter your glass.
Other Membrane Polymers and When They Are Used
Not every membrane in the water world is a modern polyamide RO element. Engineering overviews, such as those from JMark Systems, describe several other membrane polymers that appear in specific niches.
Cellulose acetate membranes were among the earliest RO materials. They use a cellulose-based layer cast on a fabric support. Compared with thin‑film polyamide, they tend to have lower salt rejection and can be more prone to fouling, but they offer good hydrophilicity and chemical resistance in certain environments. These membranes show up more often in ultrafiltration or microfiltration roles, in beverages or wastewater, than in high-rejection drinking-water RO systems.
More advanced polyamide and polyimide membranes extend this idea. Fully aromatic polyamide and polyimide membranes, for example, offer higher thermal and chemical stability and better chlorine tolerance than standard RO elements. JMark notes that these materials are used in harsh applications such as gas separations, membrane distillation, and hot or corrosive liquid filtration. They are more likely to appear in industrial or specialty systems than in a typical household RO unit.
For a homeowner or office, the key takeaway is that almost all point-of-use RO units rely on thin‑film composite polyamide elements.
Specialized polymers become relevant in industrial designs where higher temperatures, aggressive solvents, or unusual feed waters demand them.
Piping and Distribution: Getting Water From A to B Safely
Once the membrane has done its job, purified water still has to travel through tubing, manifolds, and distribution loops. This is where the material story gets nuanced, because what works well for municipal cold water does not necessarily work for RO or RO/DI product water.
Copper, Brass, and PVC: Common But Often Poor Matches for RO/DI
In traditional plumbing, copper and brass are staple materials. However, ASPE strongly discourages copper in RO/DI systems. With mineral-starved water, copper ions readily leach into the water, undermining purity and potentially causing health concerns in sensitive applications. Brass performs somewhat better but is still not recommended where high-purity RO/DI water is required.
PVC is another widely used piping material, especially schedule 80 PVC in industrial and mechanical rooms. ASPE guidance cautions that schedule 80 PVC is not a good fit when deionization is present. Aggressive DI water can extract plasticizers and other additives from PVC. This both weakens the pipe and introduces organics into the water. For single-stage RO systems without DI, PVC can be acceptable, but once you move into higher-purity territory, it is wise to look at other plastics.
This does not mean that every inch of copper or PVC feeding your under-sink unit must be replaced. It does mean that the distribution loop that carries low-mineral RO or RO/DI water should avoid materials that are known to leach into aggressive water. Hospitals and labs have learned this lesson the hard way, and their practices are a useful benchmark for residential upgrades.
PEX and Polypropylene: Practical High-Purity Plastics
Cross‑linked polyethylene (PEX) has emerged as a strong performer for RO and RO/DI lines. ASPE reports that PEX resists corrosion, does not significantly accumulate contaminants, and tolerates constant exposure to treated water without breaking down. It has become a go‑to choice for hospital RO/DI piping in many projects, precisely because it strikes a balance between chemical resistance, flexibility, and cost.
Polypropylene (PP) is another workhorse plastic in high-purity water. ASPE notes that PP piping is recommended for Type II and Type III water systems, where high—but not ultra‑high—purity is required. PP supports tight limits on conductivity, resistivity, and total organic carbon in those systems. Its main drawback is not water-related at all: it does not meet some flame and smoke ratings such as ASTM E84 25/50, so designers must be cautious when routing PP piping through plenums or other air-handling spaces.
For home and office RO systems, PEX and PP are attractive options for the distribution side of the system. They are already widely used in medical and lab settings that demand better-than-drinking-water purity. They also avoid some of the leaching and corrosion problems seen with copper, brass, and PVC under low-mineral water.
PVDF: Ultra-Pure and Ultra-Specialized
Polyvinylidene fluoride (PVDF) sits at the top end of plastic piping for ultra‑pure water. ASPE recommends PVDF for Type I water systems, where extremely high resistivity and very low total organic carbon are required. To meet standards like AAMI/TIR 34 in medical applications, PVDF systems often use bead‑and‑crevice‑free (BCF) joints. Those continuous welds eliminate tiny crevices where bacteria could grow.
PVDF is expensive, and ASPE points out that it is usually reserved for the rare cases where water purity approaches the highest resistivity levels. For a residential kitchen or a typical office hydration station, PVDF would be overkill. But in a research lab, semiconductor facility, or certain hospital applications, it can be the material that keeps ultra‑pure water truly ultra‑pure.
Stainless Steel Piping: Powerful but Not Plug-and-Play
Stainless steel is often treated as a universal solution for water systems, but the reality is more complex. Brown and Caldwell’s guidance for water and desalination industries emphasizes that stainless steel’s corrosion resistance depends heavily on choosing the right grade and applying it correctly. Chloride concentration, pH, free chlorine, bacteria, and temperature all influence its performance.
Different parts of a treatment plant may require different stainless grades. Startup, shutdown, and stagnant conditions can pose higher corrosion risks than steady operation. Poor handling, welding contamination, or scratches during installation can create corrosion sites even in a high-grade alloy.
At the same time, fully stainless steel RO systems are gaining favor in hygienic industries. A technical overview from Trivon Trading describes systems built with stainless frames, housings, pressure vessels, pipelines, and fittings, typically using grades 304 or 316. In these designs, stainless components withstand high pressure, support continuous operation, and offer long service life—often on the order of a decade or two in industrial settings, compared with just a few years for some mild steel or PVC builds.
The lesson for both commercial and residential users is that stainless steel is an excellent material when correctly specified and installed. It is not automatically superior in every environment, and it is not immune to misapplication.
Storage Tanks and Pressure Vessels: Where Water Rests
Storage is where RO water often spends the most time in contact with system materials, which makes tank construction especially important for water wellness.
Residential RO Tanks: Compact and Often Overlooked
For most under-sink systems, the RO storage tank is a small, pressurized vessel that holds a few gallons of product water. Cannon Water Technology describes a typical residential tank as holding about 2–4 gallons, standing roughly 15 inches tall and 12 inches wide. Inside, an air-filled bladder maintains pressure so that water can flow to the faucet without an additional pump. The tank body is non-corrosive, often metal with a protective liner or sometimes all-plastic.
These tanks are designed for convenience and basic safety rather than ultra‑high purity. They work well in many households, but they can be a blind spot if you are trying to minimize chemical exposure. Articles on stainless steel tanks point out that plastic vessels can leach chemicals into stored water over time, especially when exposed to heat or sunlight. For a tank sitting under a cool sink, the risk is lower than for a rooftop reservoir, but it is not zero.
If a homeowner is very sensitive to taste, odor, or chemical exposure, upgrading the tank can be as meaningful as upgrading the membrane.
Stainless Steel Tanks: Hygienic, Durable, and Recyclable
Manufacturers focused on tank materials, such as Nexteel, argue strongly in favor of stainless steel for storing RO water. Their reasoning is grounded in chemistry and hygiene.
Stainless steel offers exceptional corrosion resistance, so tank walls remain stable when in prolonged contact with aggressive RO water. Its smooth, non-porous surface inhibits the buildup of bacteria, mold, and biofilm, unlike some plastic or fiberglass tanks that can harbor microbes in microscopic surface imperfections. These tanks are easy to clean and sanitize, making routine hygiene maintenance more straightforward.
From a structural standpoint, stainless steel tanks handle high pressures, temperature swings, and environmental stresses, which is relevant for both industrial skids and larger residential or light commercial systems.
They are chemically stable and inert with RO water, minimizing the chance of any reactions or leaching.
There is also an environmental angle. Stainless steel is fully recyclable, whereas plastic tanks contribute to long-term plastic waste. For users who care about both water purity and sustainability, stainless tanks align with broader goals of reducing plastic use and waste.
Aesthetically, they offer a sleek, modern look that many homeowners and businesses appreciate.
FRP and Stainless Steel Vessels in Commercial Systems
On the industrial side, pressure vessels for RO elements are commonly made from filament‑wound fiber-reinforced plastic (FRP). Kurita America notes that FRP vessels can handle pressures from about 100 up to 1,200 psi while resisting corrosion. Stainless steel pressure vessels remain important in applications where steam sterilization is needed, such as some dairy operations.
Trivon’s overview of fully stainless steel RO systems extends this concept, with entire skids built from stainless components for high-hygiene sectors like food, beverage, pharmaceuticals, and hospitals. These systems trade higher upfront cost for longer service life, easier cleaning, and regulatory compliance in environments where hygiene and reliability are non-negotiable.
For many commercial users, a mix of FRP and stainless steel makes sense: FRP for membrane housings where pressure and corrosion resistance are key, and stainless for tanks, frames, and hygienic piping in contact with finished product water.
Filter Housings and Stainless Components: Beyond the Membrane
While membranes and tanks get much of the attention, the housings, strainers, and pre/post-filters between the street supply and the faucet also contribute to water quality and microplastic load.
A detailed guide from Frizzlife explains that stainless steel filters use reusable stainless mesh or perforated elements to mechanically remove sediments, rust, and suspended solids. Unlike disposable paper or plastic cartridges, these filters are washable and reusable. The stainless alloy gives them high strength and resistance to corrosion and chemical degradation. They can survive harsh water conditions, cleaning cycles, and even high-temperature sterilization for years or decades.
Importantly for water wellness, stainless filtration media do not shed microplastics and do not leach plasticizers or other additives into water.
Frizzlife notes that stainless steel is non-reactive and accepted for food-contact applications, aligning with guidance from EPA and WHO that safe drinking water systems should use chemically stable, non-leaching materials.
Precision-engineered stainless meshes can trap particles down to a few microns while maintaining good flow. In multi-stage systems, stainless cartridges often act as the structural base and primary barrier, while secondary media like activated carbon or ceramic handle chlorine, odors, and some dissolved contaminants.
Venus Wires, a supplier of stainless filtration components, highlights several practical advantages: stainless cartridges tolerate high pressure and temperature, work in corrosive industrial fluids, and can be integrated into self-cleaning backwashing filters where a reverse flow dislodges debris. This reduces manual maintenance and keeps systems performing well even with challenging feed water.
For residential and light commercial systems, using stainless housings or pre-filters upstream of an RO unit can reduce reliance on disposable plastic cartridges and minimize the risk that the filtration media itself becomes a source of microplastics or chemical leaching.
Materials, Microplastics, and Point-of-Use Performance
Microplastics are now an unavoidable part of the drinking-water conversation. Studies summarized by Aquatech Water Systems and Orb Media have found microplastic particles in the majority of tap water samples tested globally and in an even higher share of bottled water brands. One large analysis reported particles in 93% of bottled water samples, sometimes at very high counts, with bottle caps identified as a likely source of shed plastic.
Conventional municipal plants typically remove between about 70 and more than 90% of microplastics larger than a micron, according to research cited in a PubMed Central article on point-of-use devices and in overviews from Just Plumbing AZ. Yet residual particles remain, and the distribution system and household plumbing can add more.
This is where RO and other membrane-based point-of-use devices come in. Multiple sources, including Just Plumbing AZ, Bevi, Aquatech Water Systems, and Culligan, report that RO systems can reach microplastic removal rates around 99.9% in controlled studies. A Canadian research team evaluated common pour-through filters that use combinations of granular activated carbon, ion exchange, and membrane or microfilter layers. Devices that used only carbon and ion exchange sometimes released more microplastic fragments than they removed, likely because particles accumulated and were then dislodged. Devices that combined carbon and ion exchange with a membrane—either a non‑woven layer with relatively large pores or a true microfilter with much finer pores—removed between about 78 and 86% of polyvinyl chloride fragments and 94 to 100% of polyethylene terephthalate fragments across their tested life.
The device with the smallest nominal pore size, around the sub-micron range, performed best overall, underscoring the importance of tight physical barriers. Frizzlife’s buyer’s guide on microplastics emphasizes the same point: microfiltration, ultrafiltration, and RO are far more effective for microplastics than carbon alone, especially when pore sizes are in the fraction-of-a-micron range and filters are independently certified.
At the same time, the materials within these systems matter. Bevi and a Home‑Barista forum discussion both highlight that polymer-based RO membranes and plastic tubing can shed micro- and nanoparticles as they age. Some experienced RO users therefore prefer to run finished water through a carbon post-filter and then through PEX or stainless piping, rather than relying on small generic plastic tubes and tanks of uncertain composition. Stainless steel filters and tanks, as discussed earlier, can further reduce the risk of plastics in the storage and distribution stages.
From a health perspective, researchers and organizations such as WHO are still unraveling exactly how microplastics and nanoplastics behave in the human body. However, multiple articles point to concerns around inflammation, digestive irritation, and chemicals carried on plastic surfaces, including additives such as BPA and phthalates and absorbed pollutants. In that context, material choices that both remove particles efficiently and avoid adding new plastics or chemicals downstream are a sensible precaution.
Commercial vs Residential Priorities: How Material Choices Differ
Commercial, medical, and industrial RO systems face different pressures than residential units, but they can still inform each other. The table below summarizes some of the key materials and where they tend to make the most sense, based on the sources discussed.
Component |
Common materials in practice |
Strong fit for homes and small offices |
Strong fit for commercial or high-purity systems |
Key limitations and cautions |
Membrane element |
Thin‑film composite polyamide; cellulose acetate; advanced polyamides |
Under-sink RO systems overwhelmingly use thin‑film composite polyamide, offering broad contaminant and microplastic removal |
Polyamide RO and sometimes NF elements for brackish and seawater; specialized polyimides in harsh conditions |
Polymer membranes can shed microplastics as they age; require pretreatment, monitoring, and periodic cleaning or replacement |
Distribution piping |
Copper, brass, PVC, PEX, polypropylene, stainless steel, PVDF |
PEX or polypropylene downstream of the RO unit, borrowing hospital-grade practice; short lengths of copper feeding cold water remain common |
PEX or polypropylene for RO/DI loops; PVDF with bead‑and‑crevice‑free joints for ultra‑pure Type I water; stainless where hygiene and strength are critical |
Copper and brass are discouraged for RO/DI due to leaching; PVC is not recommended when DI is present; stainless requires correct grade selection |
Tanks and vessels |
Mild steel or concrete (legacy), plastic, FRP, stainless steel |
Standard 2–4 gallon lined tanks are common; stainless tanks are preferable for those prioritizing purity and hygiene |
FRP membrane vessels for high-pressure duty; stainless tanks and frames for hygienic industries and steam-sterilized systems |
Plastic tanks can leach chemicals, especially with heat; mild steel and concrete are vulnerable to RO corrosion; stainless has higher upfront cost |
Filter housings and cartridges |
Disposable plastic housings and cartridges; stainless mesh or cartridges |
Plastic housings remain common; reusable stainless pre-filters reduce plastic waste and potential microplastic shedding |
Stainless housings and cartridges in food, beverage, pharmaceutical, and industrial lines, often with self-cleaning designs |
Plastic cartridges can shed particles and create more waste; stainless requires proper alloy selection and cleaning protocols |
This comparison shows that many “industrial” material choices—PEX or PP piping, stainless tanks, stainless pre-filters—translate directly into more resilient, health-conscious home systems when sized appropriately.
Practical Planning for Specifiers and Homeowners
For engineers and facility managers, the first step in material selection is to define the water type and operating environment clearly. ASPE notes that mislabeling is common, with “filtered,” “RO,” “RO/DI,” and “distilled” used interchangeably in everyday conversation. Before locking in materials, it is important to confirm whether the system will deliver filtered municipal water, standard RO permeate, RO followed by deionization, or ultra‑pure Type I water. Each step up in purity brings more aggressive water and tighter material requirements.
The next step is to match materials to each segment rather than trying to find a single “best” material. Stainless may be ideal for a hygienic storage tank but unnecessary for every piece of low-pressure tubing. PEX or PP can be excellent for RO/DI loops, while FRP is a logical choice for high-pressure vessels. In hospital and lab projects, many teams follow AAMI Technical Information Reports and similar standards to align piping materials with required water types; those same documents can guide high-end commercial designs.
For homeowners, a practical approach is to focus on a few high-impact upgrades. A well-chosen under-sink RO system with a certified thin‑film composite membrane, sediment and carbon pre-filters, and a carbon post-filter is a strong foundation. Replacing generic downstream plastic tubing with PEX, choosing a stainless or high-quality lined storage tank, and installing a plastic-lined faucet specifically designed for low-mineral water are incremental steps that build on that foundation. Culligan notes that many RO filters are designed for annual or biennial replacement, and membranes often have a recommended life of several years; following those intervals helps keep both chemical and microplastic risks in check.
At every scale, independent certification remains important. Standards from ANSI/NSF, including those for particulate reduction (such as Class I particulate claims), RO performance, and microplastic-related testing, give an extra layer of assurance that a given system does more than simply rely on theoretical material properties.
Short FAQ: Materials and RO Water
Do I always need stainless steel components in an RO system?
Stainless steel is an excellent material for corrosive, high-pressure, or high-hygiene environments, and it is strongly favored in sectors such as food, beverage, pharmaceuticals, and hospitals. However, sources like Brown and Caldwell emphasize that stainless performance depends on correct grade selection and installation. For many homes and offices, a mix of good plastics such as PEX or polypropylene plus targeted stainless parts—like a storage tank or reusable pre-filter—offers a practical balance of cost, durability, and water quality.
Should I specify PVDF piping for a residential RO system?
PVDF shines in ultra‑pure water systems, such as Type I lab water lines meeting AAMI/TIR 34, where bead‑and‑crevice‑free joints help eliminate bacterial growth points. ASPE notes that it is usually reserved for those demanding applications because of its cost. For a home kitchen or most office hydration systems, PEX or polypropylene derived from hospital-grade practice is typically more than adequate.
How often should RO membranes and filters be replaced to manage microplastics and leaching?
Multiple sources stress that performance depends on proper maintenance. Bevi and others highlight that aging polymer membranes can begin shedding microplastics, and Culligan recommends changing RO pre-filters about every one to two years and membranes roughly every three to five years under typical conditions. These intervals, combined with periodic inspections, pretreatment to reduce fouling, and a carbon post-filter, help maintain both contaminant removal and control of particles shed from system materials.
Choosing materials for an RO system is ultimately about giving clean, low-mineral water a safe path from the membrane to your glass. When you align membrane type, piping, tanks, and housings with the level of purity you actually need—and maintain them with intention—you get more than impressive lab numbers. You get reliable, great-tasting, low-contaminant water that supports everyday hydration, whether you are filling a family water bottle or a hospital dialysate tank.
References
- https://www.energy.gov/femp/articles/reverse-osmosis-optimization
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10054062/
- https://aspe.org/pipeline/what-is-the-best-material-for-reverse-osmosis-water-for-hospital-equipment/
- https://nickelinstitute.org/media/1779/reverse_osmosis_which_stainless_steel_to_use_10003.pdf
- https://trivontrading.co.ke/why-a-fully-stainless-steel-reverse-osmosis-system-is-the-best-choice-for-industrial-and-hygienic-water-purification/?srsltid=AfmBOorkkxifQ7LJmFrnngM5yrKsUkagB2Ku8G71OVt79S4-xKUs6SXO
- https://www.culligan.com/blog/does-reverse-osmosis-remove-microplastics-from-drinking-water
- https://www.home-barista.com/water/plastic-micro-and-nanoparticles-in-ro-water-t101542.html
- https://www.jmarksystems.com/blog/7-types-of-ro-membranes
- https://www.justanswer.com/plumbing/pv6q3-plastic-tubes-used-reverse-osmosis-made.html
- https://www.kuritaamerica.com/the-splash/membrane-system-design-reverse-osmosis
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