Choose a water filter by what a test finds, not by what a seller offers. Sediment and carbon filters handle grit, chlorine taste and smell, and some organic chemicals. Reverse osmosis (RO) pushes water through a membrane and can sharply reduce lead, nitrate, fluoride and sodium, usually at one tap. Neither softens a whole house, and neither makes unsafe water safe. If you only care about what you drink, a certified filter at the kitchen tap usually costs less than whole-house treatment, and it sits after your pipes, which matters for lead. This page matches each problem to a tool, then shows what to read next.
This is general information, not medical or professional advice. WaterPlain has no lab and tested none of these systems: we compare published certifications, data sheets and agency guidance. Take well test results or any illness to your state or county health department or a certified lab.
Start with a test
You may not need any of this. EPA says a tap filter or pitcher “may be all you need”, and the CDC says that if your water is free of harmful germs and chemicals, “you may not need a filter.” On city water, read your utility’s annual water quality report. On a well, use a state-certified lab; our guide to well water tests covers what to order. Write down the contaminant and its level: those two facts decide what comes next.
Which tool for which problem
| Your problem | Where to start | Worth knowing |
|---|---|---|
| Chlorine taste in drinking water only | A carbon filter at the tap or a pitcher | Not RO, and not whole-house |
| Grit or cloudy water at every tap | A whole-house sediment filter | It removes particles only, no dissolved chemicals |
| Lead from your plumbing | A filter at the tap certified to NSF/ANSI 53 with a lead claim, or RO with a lead claim | Check the exact model |
| Nitrate, arsenic, fluoride or salt confirmed by a test | Your health department on any health result, then point-of-use RO as a strong candidate | Check your level against the data sheet. Arsenic form matters |
| PFAS reported by your utility or a lab | RO or carbon with a named claim, usually at the tap | Our PFAS filter guide explains what the listings prove |
| A solvent or radon on a test report | Health department advice, then usually whole-house carbon or aeration | These are breathed in the shower too, so one tap may not be enough. RO does not remove dissolved gases |
| Coliform or E. coli | Your state or county health department, before you buy anything | Standard filters do not treat these. Do not rely on RO |
| Hard water, scale | A softener, not a filter | Our softener and filter comparison matches each symptom to its fix |
| Rust stains or a rotten-egg smell on a well | Not RO, and not a standard carbon unit | Use well treatment matched to your test |
| A salty or very high-TDS well | The clearest case for whole-house RO, after pricing a new well or a public connection | Softeners do not remove dissolved salt |
On nitrate, even with home treatment, Minnesota’s health department recommends that “no babies under six months old drink the treated water”, because bottled water may be safer if the treatment stops working.
Four guides, in reading order
- What reverse osmosis is and what it removes. Start here if RO is on the table. It goes through each substance, including where sources disagree.
- Choosing a home RO system from published specs. Read this once a test points to RO. It shows why a “75 GPD” unit may test at about 21 gallons a day.
- Whole house water filters. Read this if the problem reaches beyond what you swallow. It covers types, flow and ten years of replacements.
- Whole-house RO, and who really needs it. Read this before you sign a quote. Most homes should not buy one.
One tap or the whole house
Point-of-use treats one tap; point-of-entry treats water where it enters the home. More coverage is not automatically better.
- Lead. EPA’s lead filter guide leaves out whole-house filters “because they don’t remove lead that might be coming from any lead-containing plumbing inside the building.” Brass faucets and lead solder sit after a filter at the main, so the CDC recommends a point-of-use filter.
- Germs. The CDC says removing chlorine with a whole-home filter may let more germs grow in your plumbing, because the water no longer carries that protection through your pipes.
- Flow. Two showers and a faucet at standard flow come to 7.2 gallons a minute. Two whole-house systems with health claims are rated at 4 and 4.82, so a filter can become the bottleneck.
- Wells. Most whole-house marketing is built around chlorine, and well water normally has none unless you add it. So a chlorine-rated carbon tank may solve nothing. That is our reading, and a lab report should settle it.
Whole-house RO goes further still. It is a small treatment plant, with pumps and a storage tank. EPA calls these systems “typically not recommended for most treatment applications”. A family of four would send about 28,000 to 256,000 gallons a year to the drain, depending on recovery.
What certification proves
Certification belongs to one model and one claim. The standards you will see are NSF/ANSI 42 for taste and odor, 53 for health claims and 58 for RO. EPA also names WQA, IAPMO, CSA and UL as certifiers, so the logo may not say NSF.
Public records on 2 November 2026 show why the wording matters:
- “Certified to 58” can mean TDS only. Of about 340 plumbed-in model names in NSF’s RO directory, about 210 are listed for total dissolved solids (TDS) reduction and nothing else, and none mentions PFOA or PFOS.
- Whole-house health claims are rare. NSF’s point-of-entry list under standard 42 shows 57 products. Its standard 53 list shows four, all for volatile organic chemicals. Other certifiers may list others.
- Certified does not mean below EPA’s PFAS limit. Federal regulation sets 4.0 parts per trillion each for PFOA and PFOS in public water; EPA has proposed changes, and none is final. Two whole-house data sheets list pass levels of 20 and 70. In a May 2026 notice, EPA said the NSF/ANSI standard “does not currently meet the PFOA and PFOS MCLs”, meaning those limits.
So open the performance data sheet, find your contaminant by name, and confirm the exact model in the certifier’s directory. If your utility uses chloramine, ask before buying: EPA says it is harder to remove than chlorine and that RO does not remove it, though water that meets standards does not need it removed.
What each option costs
These are dated published figures, not quotes, and they count different things. Get your own in writing.
| Option | To buy | Over the years |
|---|---|---|
| Under-sink filter | $80 to $200 or more, plus a lead-free faucet (EPA lead filter guide, February 2024 prices) | $50 to $100 cartridges, lasting 6 to 24 months or more |
| Point-of-use RO | About $180 to upwards of $700 (EPA, 2024). $300 to $2,000 by daily output (Penn State, July 2026) | About $1,110 to $1,360 in all over five years, in our example at Penn State’s floor prices for PFAS-certified units, before installation |
| Whole-house filter | $500 to $1,500 (Penn State). Installing one “generally costs several thousand dollars” (EPA, 2024) | About $5,370 in all over ten years for one long-life carbon tank at listed prices, for four people, before labor |
| Whole-house RO | $7,674 to $11,844 set up, from Crystal Quest’s 2026 seller figures, before tests, electrical, drain and permit work | About $16,000 to $32,000 in all over ten years on city water and sewer, in our example, before electricity |
EPA says typical point-of-use RO runs at 10% to 20% efficiency, or four to nine gallons down the drain per gallon treated. The WaterSense minimum of 30% means 2.3 gallons. On septic, reject water adds to the load, so ask your local health department before buying.
Keep it working
EPA says unmaintained systems “may make water quality worse”, so budget the upkeep before you buy.
- Change parts on schedule. Follow the maker’s dates, and count gallons as well as months in a busy home.
- Check your water suits the unit. RO manuals we read ask for at least 40 psi, about 10 grains per gallon of hardness at most, and very little iron. If hardness is over that line, our RO and softener comparison works through the choice.
- Test after installing. Send a sample from a tap you use to a lab. A TDS meter is a cheap running check on an RO membrane, but it won’t confirm that lead, nitrate or arsenic is gone.
Facts on this page come from the guides linked above, which were checked against primary sources on 2 November 2026. Every figure is checked against its source. We use no affiliate links or paid placements.
