Start with your water report and the specific thing you want to change. Then check that a system fits your counter and your routine, confirm that its certification covers that exact model and that exact substance, and add up its filters over three years. A format or brand name alone tells you very little.
Do you need a filter at all?
The CDC says that if your tap water doesn’t contain harmful germs or chemicals, you may not need a filter. Minnesota’s health department, writing for its own residents, says most of them don’t need home treatment for health reasons. Many people still want a filter for taste or for peace of mind, and that’s a fair reason to buy one, as long as you know that’s the reason.
Find out what’s in your water first:
- On a public water system, read your utility’s annual Consumer Confidence Report.
- On a private well, the CDC advises testing at least once a year.
- In an older building, remember that the report describes the utility’s water, not your pipes. EPA explains that lead usually enters drinking water through plumbing corrosion, including lead service lines and older fixtures and solder. Only a test at your tap tells you what’s happening there.
What do you want the filter to change?
Different goals point to different products, and no single home unit does everything. Minnesota’s health department puts it plainly: no single treatment unit can remove all contaminants.
| If your goal is | Look for | Keep in mind |
|---|---|---|
| Better taste or less chlorine smell | NSF/ANSI 42, the standard for aesthetic effects | This standard says nothing about health-related contaminants. |
| Reducing a specific contaminant | A certified claim for that substance, usually under NSF/ANSI 53 or 58 | Check the named substance. The standard’s number alone doesn’t tell you. |
| Reducing PFAS | A claim that names the PFAS you care about | Minnesota notes that these certifications, as of April 2024, didn’t yet show reduction to EPA’s newer levels. |
| Softer water | A softener, not a filter | Softeners swap hardness ions for sodium or potassium. They’re a different device under a different standard. |
| A lower TDS meter reading | Think again about the goal | EPA’s 500 mg/L figure for TDS is a non-mandatory guideline for aesthetic effects. A TDS reading doesn’t tell you whether water is safe. |
What does “countertop” actually mean?
The word covers products that ask very different things of you.
- Pitchers and simple gravity filters have no power or plumbing. The CDC says most pitcher and refrigerator filters mainly improve taste and smell, and most aren’t designed to remove germs.
- Fill-by-hand reverse osmosis units plug into the wall and need no plumbing. You pour tap water in and carry the leftover water back to the sink. The AquaTru Classic and AquaTru Carafe are examples.
- Connected countertop units sit on the counter but still need some installation. The Waterdrop K6, for example, is described as a 15-minute DIY installation designed to fit standard kitchen faucets.
So if you rent or don’t want to touch your plumbing, confirm how a unit gets its water. “Countertop” doesn’t settle it.
Measure before you compare
A filter you resent using is a poor buy, so check the fit before you check the features. As examples, here are the published sizes of two no-plumbing units:
Fit details for two no-plumbing units
| Specification | AquaTru Classic | AquaTru Carafe |
|---|---|---|
| Size (W x D x H) | 12 x 14 x 14 in[1] | 7.5 x 14 x 13 in[2] |
| Weight | About 17 lb[1] | About 9 lb[2] |
| Treated water held | 0.75 gal[1] | 0.5 gal[2] |
| Tap water tank | 1 gal[3] | 0.66 gal[2] |
| Power | 120 V, 60 Hz wall plug[4] | 120 V, 60 Hz wall plug[5] |
| Plumbing connection | None required[1] | None required[2] |
- AquaTru Classic, size (w x d x h): An undated AquaTru specification sheet hosted by a retailer lists 11.5 in wide and 16.3 lb. We use the current product page.
- AquaTru Classic, tap water tank: From an undated manufacturer sheet. The current product page does not state tap-tank size.
Sources for this table (5)
- AquaTru Classic product page, AquaTru. Accessed November 2, 2026.
- AquaTru Carafe product page, AquaTru. Accessed November 2, 2026.
- AquaTru Model AT2000, AT2010 Specifications, hosted by The Home Depot, AquaTru. Accessed November 2, 2026.
- AquaTru Countertop Model Performance Data Sheet, AquaTru, version 10.24.R4. Accessed November 2, 2026.
- AquaTru Carafe Model Performance Data Sheet, AquaTru, version 09.25.R5. Accessed November 2, 2026.
Measure these at home:
- Footprint and height where the unit will actually sit, including the clearance under any wall cabinets.
- Room to work. On a fill-by-hand unit you lift a tank out and carry it. AquaTru’s manual says to remove the tap tank to refill it, and to discard what’s left in it each time.
- The sink. Check that the tank fits under your faucet.
- The outlet. Check there’s one close enough. A plugged-in unit takes up an outlet for as long as it’s in use.
How to read a certification claim
Three things are worth knowing:
- The numbers aren’t a ranking. NSF notes that standard numbers don’t indicate quality levels. They cover different things.
- Certified doesn’t mean it removes everything. NSF says certification doesn’t mean a unit reduces all possible contaminants, so check the specific ones you care about.
- It belongs to a model, not a brand. A brand can make a certified unit and an uncertified one. Check the model number at the certifier’s public listing, such as the IAPMO R&T directory or NSF’s, instead of relying on a logo on a sales page.
Documents can also lag behind each other. AquaTru’s Carafe data sheet states certification, and a directory search for that model returned active listings, yet its FAQ still called the certification pending when we checked. When sources disagree, the certifier’s record is the one to trust.
What reverse osmosis does and doesn’t do
Reverse osmosis (RO) is common in this category, and easy to oversell. The CDC says RO removes germs and some chemicals, including lead and copper, and may reduce arsenic and fluoride. It’s still not a universal solution, and three limits matter when you’re comparing units.
It sends water down the drain. EPA reports that typical plumbed point-of-use RO systems send 5 gallons or more to the drain for each gallon treated, and some up to 10. It also says RO isn’t needed for every application, and that filtration may be enough. Those figures describe plumbed systems. Fill-by-hand units state their own, such as 75% efficiency for the Classic and 63% for the Carafe. Those are manufacturer figures, and we haven’t measured them.
It has limits on the water going in. Data sheets set conditions. For both AquaTru models, the Classic and Carafe sheets list a maximum hardness of 10 grains per gallon, or 171 mg/L. The USGS scale calls 121 to 180 mg/L hard, so plenty of ordinary tap water comes close. AquaTru’s FAQ warns that harder water can plug the RO filter unless it’s softened first or you descale regularly. Check your water report for hardness before you buy any RO unit.
It isn’t a disinfection system for unsafe water. The Classic’s data sheet says not to use it with water that is microbiologically unsafe without disinfection. If you’re dealing with a boil-water notice or a contaminated well, follow your local health authority’s guidance, not a product page.
Count three years, not one purchase
Replacement filters can cost more than the machine over time, and the cheaper unit doesn’t always stay cheaper. Our guide to comparing replacement-filter costs walks through the method with real part schedules.
Change filters on schedule too. EPA explains that carbon filters can clog once they pass their rated volume, and the CDC says to follow the manufacturer’s replacement schedule. If you can’t keep up with the routine, the filter won’t deliver what you bought it for.
Questions to answer before you buy
- Which specific substances or taste issues am I trying to address, and what does my water report or test say about them?
- Is this exact model number listed by the certifier for those substances?
- Does my water meet the limits on the data sheet, especially hardness?
- Does it fit the space, including the room I need to lift tanks or change filters?
- Will I keep up with the refilling and cleaning it needs?
- Which replacement parts fit it, how much do they cost, and how soon will I reach their limits?
- Are there return terms if it doesn’t suit my kitchen?
If you’ve already narrowed it to a format, see filters for apartments or countertop vs. under-sink.