List every replacement part for the exact model, then work out how many of each you'll buy over three years, based on your daily use and whichever limit each part reaches first, time or gallons. Add the purchase price. A cheaper unit with lower-rated filters can cost more once your usage goes up.
Step 1: List the parts for the exact model
Don’t assume parts carry over within a brand. AquaTru says the Classic isn’t compatible with Carafe filters, and it sells separate parts labeled Carafe only. A system may have one filter or several, and each may be replaced on its own schedule. Write down every one, with its part name.
Step 2: Find both limits for each part
Most filters have a time limit and a gallon limit, and you replace the filter at whichever comes first. Here’s how that looks for two models:
| Filter | AquaTru Classic | AquaTru Carafe |
|---|---|---|
| Pre/carbon | 6 months or 600 gal | 6 months or 300 gal |
| VOC carbon | 12 months or 600 gal | 12 months or 300 gal |
| Reverse osmosis | 24 months or 1,200 gal | 24 months or about 600 gal |
The Carafe’s filters are rated for half the gallons of the Classic’s. At light use that makes no difference, since the time limits come first. At heavy use it matters a lot.
Step 3: Estimate your daily use honestly
Count the water you’d really run through it: drinking, coffee and tea, cooking, and any bottles you fill. Measure for a few days if you’re unsure. Most people should work out a low and a high number, because your answer can change which limit applies.
To see where the switch happens, divide a filter’s gallon limit by the days in its time limit. A 600-gallon, 6-month filter reaches its gallon limit first if you use more than about 3.3 gallons a day. A 300-gallon, 6-month filter gets there at about 1.6 gallons a day.
Step 4: Multiply it out over three years
For each part, work out how many intervals fit into 36 months at your usage, then remember that the set in the box usually covers the first interval. AquaTru says its units come with one set of filters, but check this for whatever you’re buying.
Here’s that calculation applied to two models. Quantities come directly from the published limits. Dollar amounts appear only while our price check is less than 30 days old.
Filter purchases and cost over 3 years, by daily use
| Assumption | AquaTru Classic | AquaTru Carafe |
|---|---|---|
| Purchase price | $475.00[1] | $375.00[2] |
| Rated filter life, whichever comes first | Pre/Carbon: 6 months or 600 gal; VOC Carbon: 12 months or 600 gal; Reverse Osmosis: 24 months or 1,200 gal[3][4][5] | Pre/Carbon: 6 months or 300 gal; VOC Carbon: 12 months or 300 gal; Reverse Osmosis: 24 months or 600 gal[6][7] |
| Replacement filter prices | Pre/Carbon: $29.95; VOC Carbon: $39.95; Reverse Osmosis: $59.95[3][4][5] | Pre/Carbon: $29.95; VOC Carbon: $39.95; Reverse Osmosis: $59.95[8][9][7] |
| Using 0.5 gal/day | 3-year total $764.60Filter spend $289.60: 5 Pre/Carbon, 2 VOC Carbon, 1 Reverse Osmosis | 3-year total $664.60Filter spend $289.60: 5 Pre/Carbon, 2 VOC Carbon, 1 Reverse Osmosis |
| Using 1 gal/day | 3-year total $764.60Filter spend $289.60: 5 Pre/Carbon, 2 VOC Carbon, 1 Reverse Osmosis | 3-year total $704.55Filter spend $329.55: 5 Pre/Carbon, 3 VOC Carbon, 1 Reverse Osmosis |
| Using 2 gal/day | 3-year total $804.55Filter spend $329.55: 5 Pre/Carbon, 3 VOC Carbon, 1 Reverse Osmosis | 3-year total $1,044.15Filter spend $669.15: 7 Pre/Carbon, 7 VOC Carbon, 3 Reverse Osmosis |
| Using 4 gal/day | 3-year total $1,144.15Filter spend $669.15: 7 Pre/Carbon, 7 VOC Carbon, 3 Reverse Osmosis | 3-year total $1,773.25Filter spend $1,398.25: 14 Pre/Carbon, 14 VOC Carbon, 7 Reverse Osmosis |
- Each filter is replaced at its stated time limit or gallon limit, whichever comes first. The set that ships with the purifier covers the first interval.
- Excludes sales tax, shipping, electricity, tap water, descaling supplies and any early replacement caused by hard water or poor feed-water quality. Electricity is left out because neither manufacturer page we checked publishes wattage.
- Manufacturer list prices checked on November 2, 2026. Retail prices change: confirm before you buy.
Sources for this table (9)
- AquaTru Classic product page, AquaTru. Accessed November 2, 2026.
- AquaTru Carafe product page, AquaTru. Accessed November 2, 2026.
- Classic Pre/Carbon Filter, AquaTru. Accessed November 2, 2026.
- Classic VOC Carbon Filter, AquaTru. Accessed November 2, 2026.
- Classic Reverse Osmosis Filter, AquaTru. Accessed November 2, 2026.
- AquaTru Carafe Owner's Manual, AquaTru, version 08.22.R3. Accessed November 2, 2026.
- Carafe ONLY Reverse Osmosis Filter, AquaTru. Accessed November 2, 2026.
- Carafe ONLY Pre/Carbon Filter, AquaTru. Accessed November 2, 2026.
- Carafe ONLY VOC Carbon Filter, AquaTru. Accessed November 2, 2026.
As of our check on November 2, 2026, the pattern is clear: the Carafe costs less to buy and stays cheaper at up to 1 gallon a day, but by 2 gallons a day it has become the more expensive system, because it needs more filters at the same part prices. At 4 gallons a day it needs at least twice as many of each type. Neither result makes one a better product. It only means your usage has to go into the sum.
Step 5: Check the packs, but do the math
Bundles aren’t always discounts. When we checked, the two-year filter pack for the Classic cost exactly what its contents cost separately. It may still be convenient, and prices change often, so add up the parts each time.
Also see if the bundle matches your use. A pack sized for time limits won’t last as long if you hit gallon limits first.
Step 6: Add what the table leaves out
Our table leaves these out because we can’t price them for you:
- Tax and shipping, which vary by address and order size.
- Electricity. We didn’t find wattage on the manufacturer pages we checked, so we haven’t estimated it.
- Tap water sent to the drain. Stated efficiency is 75% for the Classic and 63% for the Carafe. That works out to about 1.33 and 1.59 gallons of tap water for each treated gallon.
- Descaling supplies and other accessories, which may matter in harder water.
- Early replacement. Rated life isn’t a guarantee. AquaTru warns that water over 10 grains per gallon of hardness can plug the RO filter and mean more frequent replacement unless it’s softened or descaled. EPA also notes that carbon filters clog after their rated volume and have a shelf life.
Watch for numbers that don’t agree
Filter life is often stated differently in different places, even by the same seller. Waterdrop’s M6RFL replacement page for the M6SL shows both 528 gallons and 1,100 gallons, and the M6SL’s product page says 12 months or 1,100 gallons. At steady use, a difference that large could change how often you buy filters. We haven’t resolved it, so we don’t use the figure in any cost table on this site. If you find a conflict like this, ask the seller, and do your sums with the lower number until you hear back.
Don’t stretch filters to save money
It’s tempting to run a filter past its limit, but the CDC says to change filters on the manufacturer’s schedule. If the real cost of keeping up looks too high, that’s useful to know before you buy: it’s a reason to choose a different system, or to ask whether you need one at all.