Best-Value Remineralizing Under-Sink RO: Purchase Prices and 5-Year Filter Costs

Within a $200 to $1,200 purchase budget, the Viomi M1 has the lowest five-year cartridge spending of any tankless remineralizing RO system in this comparison, $349.97, only $6 more than the tanked iSpring RCC7AK's $343.97. The three other tankless systems, the Waterdrop G5P700A, the iSpring RO500AK-BN, and the Waterdrop G3P600 with an MNR35 mineral add-on, are all priced below the Viomi M1 but spend more on cartridges over the same five years. For the lowest price to get started, the two tanked systems lead: the iSpring RCC7AK at $241.99 and the APEC ROES-PH75 at $268.99. Across these six systems, five-year cartridge spending runs from $283.70 to $737.86, a cartridge cost of roughly $57 to $148 per year as a 5-year average, and the bill arrives in uneven bursts in the years when a membrane is due.

Built-In Remineralization vs. Add-On Mineral Kits

Reverse osmosis removes most dissolved minerals along with contaminants. A remineralization stage adds minerals such as calcium and magnesium back after the membrane, which changes taste and raises the TDS reading. There are two ways to get it:

• Built in. The mineral stage ships as part of the system and is replaced on the system's own schedule. Sometimes it is a dedicated cartridge; sometimes it is combined with another filter.
• Added on. A separate mineral cartridge is plumbed in after the RO output of a system that does not mineralize on its own. The cartridge is a separate purchase with its own replacement interval.

This article prices both, but keeps them apart because the add-on route puts one more cartridge on the replacement schedule.

The Shortlist Inside a $200 to $1,200 Budget

Each system below is sold on its brand's official website within the budget and includes remineralization.

Prices from each brand's official website, October 2026.

Waterdrop's X12, which also mineralizes, is listed at $1,299 and falls just outside this budget.

Year-by-Year Filter Spending, Years 1 to 5

The figures below follow each brand's published replacement intervals and current cartridge prices, and they show replacement-cartridge purchases by the year they are bought. Three rules keep the comparison even:

1. The cartridges in the box are not counted again. Spending starts when a cartridge first reaches its rated interval.
2. Each cartridge is replaced at the longest interval the brand states. Where a brand gives a range, such as "6 to 12 months," the upper end is used.
3. A replacement belongs to the year it falls in. A 6-month cartridge is first replaced in year 1; a 24-month cartridge is first replaced at the start of year 3.

How each row was built:

• Viomi M1: the Viomi M1 PCB filter (99.99)lastsupto2yearsandthe[ViomiM1ROfilter](https : //water.viomi.com/products/m1 − ro − filter − replacement − 48 − month)(149.99) up to 4 years.
• iSpring RCC7AK: iSpring's manual rates the sediment filter up to 6 months; the GAC, CTO carbon block, post carbon, and FA15 alkaline filters up to 1 year; and the RO membrane up to 3 years. iSpring sells replacements for this system as sets, so the row records set purchases: its 6-month F4AK set (41.99)inyear1, its3 − yearF28K75set(220.99, which includes one membrane) at the start of year 2, and its 1-year F9K set ($80.99) in year 5. Cartridges from each set are kept and installed as they come due, so years with no purchase still include filter changes.
• APEC ROES-PH75: stages 1 to 3 and the stage 6 pH+ filter are replaced together with APEC's FILTER-SET-ESPH (55.95)every12months.Inyear5, the75GPDmembrane(44.95) and the stage 5 inline carbon filter ($14.95) also reach their 4-year interval for city water.
• Waterdrop G5P700A: the G5P700A-CF filter (39.99)isratedupto6monthsor1, 056gallons, andtheG5P700 − ROfilter(99.99) up to 24 months or 2,112 gallons.
• iSpring RO500AK-BN: FCF500 composite filter (45.99)upto6months, FCA500carbonalkalinefilter(57.99) up to 12 months, and MRO500 membrane ($91.99) at 24 to 36 months (36 used here).
• Waterdrop G3P600 + MNR35: CF filter (29.99)upto6monthsor550gallons, CBfilter(29.99) up to 12 months or 1,100 gallons, MNR35 remineralization filter (29.99)upto12monthsor1, 100gallons, andG3P600ROfilter(109.99) up to 24 months or 2,200 gallons.

Notice how uneven the yearly bill is. A system with a quiet year 4 can still have a heavy year 5 when the membrane and pre-filter come due together. When budgeting, look at the five-year cartridge total and the cartridge cost per year (5-year average), not just year 1.

What "Best Value" Can Mean

There is no single winner, because "value" means something different depending on what you want to spend less of: money up front, cabinet space, or maintenance attention.

Lowest purchase price: tanked systems

The iSpring RCC7AK (241.99)andAPECROES − PH75(268.99) are the least expensive ways into remineralized RO water, and both stay among the lowest on five-year filter spending. Both use standard 10-inch by 2.5-inch sediment and carbon prefilters, and both brands sell multi-stage replacement sets. The RCC7AK runs without electricity. The trade-off is space and output: each has a storage tank under the sink and a 75 GPD rating, so water is drawn from what the tank has stored. For more context on how older tank-based systems compare on cost, see Viomi's RO system cost comparison.

No tank under the sink: tankless systems with mineral stages

The Waterdrop G5P700A (359.99)andiSpringRO500AK − BN(692.99) remove the tank and produce water on demand. Using their listed cartridge prices and schedules, five-year cartridge spending comes to $559.89 and $737.86. Both include a 6-month cartridge: the G5P700A's mineralizing CF filter, and the RO500AK-BN's FCF500 composite filter, which pairs with a 12-month FCA500 mineral filter.

Fewest cartridge changes: long cartridge intervals

The Viomi M1 (regular price $899.99) has the lowest five-year cartridge spending of any tankless system in the table, $349.97, nearly level with the iSpring RCC7AK's $343.97. Only two cartridges sit in the system, and both run long: a PCB filter that doubles as the mineralization stage, rated up to 2 years, and an RO filter rated up to 4 years. Over five years, that is three replacement cartridges in total.

Long intervals only save effort if you know when they end, and the Viomi M1 tracks remaining filter life in three places: the touchscreen faucet, the main unit, and the Viomi App, which sends replacement reminders. Tap and purified TDS appear on the faucet as well, and once "Multi-device Mode" is switched on in the app, a refrigerator or ice maker can draw from the system through a standard tubing connection.

Installation suits a standard kitchen setup. Like the other tankless systems here, it runs on household power from a standard outlet in the cabinet; where a garbage disposer is plugged in there too, a separate, constantly powered outlet for the purifier is the right setup. Two holes complete the job: one of 1 to 1.5 inches in the countertop or sink for the faucet, and a 1/4 inch hole in the drain line.

Add-On Kits: When a Separate Mineral Cartridge Makes Sense

An add-on kit suits someone who already owns, or prefers, an RO system without a mineral stage. Waterdrop sells its G3P600 bundled with the MNR35 remineralization filter for $566.99, and the MNR35 is also sold on its own for $29.99. In this calculation, the MNR35 is a fourth cartridge with a 12-month or 1,100-gallon rating, adding $29.99 in each of years 2 through 5, and the G3P600 route's five-year cartridge spending comes to $729.81.

If you are buying new, note how the mineral stage is packaged: combining mineralization with another cartridge avoids a separate mineral-cartridge replacement, as with the Viomi M1 PCB filter and the Waterdrop G5P700A CF filter.

Run the Numbers for Your Own Household

Several cartridges in this comparison, including Waterdrop's, are rated by time or gallons, whichever comes first. For those, estimate your own replacement interval in days:

Replacement interval (days) = the smaller of (rated gallons ÷ gallons you use per day) and the rated time limit converted to days.

Cartridges rated by time alone follow their stated interval.

Two worked examples:

• Waterdrop G5P700-RO, rated 24 months or 2,112 gallons. At 2 gallons of RO water a day, 2,112 ÷ 2 = 1,056 days, so the 24-month limit arrives first. At 4 gallons a day, 2,112 ÷ 4 = 528 days, about 17 months, so the gallon limit arrives first and the filter is replaced roughly 7 months early.
• Waterdrop G3P600 CF filter, rated 6 months or 550 gallons. At 3 gallons a day, 550 ÷ 3 is about 183 days, almost exactly six months, so about 3 gallons a day is the approximate break-even point. Well above that, the gallon limit sets the pace.

Then multiply each cartridge's price by the number of replacements in your time frame, skip the cartridges that came in the box, and add the years together; for systems sold in multi-cartridge sets, count the sets you would buy. A spreadsheet with one row per cartridge gives you a five-year number based on your water use instead of anyone else's.

For background on how different brands approach mineral stages, Viomi's overview of RO brands that offer remineralization filters covers the options in more depth.

FAQ

How often is the mineral cartridge replaced?

It depends on where the mineral stage sits. On the Viomi M1, mineralization is part of the PCB filter, rated up to 2 years. The iSpring RCC7AK's FA15 alkaline filter is rated up to 1 year, the APEC ROES-PH75's pH+ filter 6 to 12 months, the iSpring RO500AK-BN's FCA500 up to 12 months, and the Waterdrop G5P700A's mineralizing CF filter up to 6 months. Waterdrop's add-on MNR35 is rated for 12 months or 1,100 gallons.

Will remineralization change the TDS reading on my faucet display?

Yes. Adding minerals back raises total dissolved solids, so a remineralizing system reads higher than plain RO water. Viomi notes that the Viomi M1's purified TDS reading is naturally higher than standard RO water because minerals are intentionally added back, which reflects the remineralization stage rather than a change in filtration. Shown beside the tap reading on the faucet, the purified number gives a quick view of the RO stage at work, with the added minerals lifting it above plain RO water.

Will a large household need to replace filters sooner?

Cartridges with a gallon rating are replaced early once daily use passes their break-even point, which you can find by dividing the rated gallons by the rated days: 2,112 gallons over 24 months works out to about 2.9 gallons a day, and 550 gallons over 6 months to about 3 gallons a day. A five-person family that drinks and cooks with RO water can run the formula above before comparing yearly costs.

Can I add a mineral cartridge to any RO system?

Add-on mineral cartridges sit after the RO output. Waterdrop sells the MNR35 for its under-sink RO systems, including the G3P600 bundle compared here.

Weighing Purchase Price Against Five Years of Cartridges

Among the six systems compared, the tanked APEC ROES-PH75 and iSpring RCC7AK have the two lowest totals for purchase plus five years of cartridges, for kitchens with room for a storage tank. Going tankless raises the purchase price, and from there the cartridge schedules separate the options: the Viomi M1 holds five-year cartridge spending to $349.97 with three replacement cartridges in total, the Waterdrop G5P700A starts lower at $359.99 but replaces its mineralizing filter every 6 months, and an add-on mineral route such as the Waterdrop G3P600 with MNR35 puts one more cartridge on the calendar. Whichever system you choose, run the replacement formula with your household's daily RO use to account for any gallon-rated cartridges that reach their capacity limit before their time limit.