A Five-Year RO Ownership Cost Worksheet

Five years of owning an under-sink RO system adds up to the purchase price, every cartridge bought after the first set, and the extra water and electricity the system uses along the way, and in the worked examples here the first two lines make up nearly all of the total. At regular prices on water.viomi.com, the Viomi B6W comes to $589.93 for the system plus five years of cartridges. The Viomi M1, whose cartridges are rated for up to two and up to four years, needs three replacement cartridges in the same period at those rated intervals.

The Worksheet, Line by Line

Installation sits at zero in the example because the systems in this worksheet are sold for owner installation. The Viomi V6 PRO and Viomi V8 PRO, for instance, ship with the faucet, tubing and fittings for the hookup, and a step-by-step installation video walks through the job. A household that hires a plumber enters that quote on this line for the system it chooses.

The two example rates are placeholders. A household's own water bill lists its combined water and sewer charge, usually per 1,000 gallons, and its electric bill lists the price per kWh. The water line counts only the extra water an RO system sends to the drain, since the purified water itself replaces water the household would drink or cook with anyway.

Regular Prices and Replacement Rules Used Here

Prices are the regular, non-promotional prices on each brand's own store. Where a system was on promotion, the worksheet uses the regular price shown alongside it, so the comparison does not depend on the week it was made. Each cartridge price is for the replacement made for that exact model, such as the Viomi V6 PRO RO600 for the Viomi V6 PRO.

All six are tankless under-sink RO systems, which keeps the comparison within one configuration.

For price ranges across a wider set of brands, including tank-based and dealer-installed systems, see Reverse Osmosis System Cost Comparison: APEC, iSpring, Culligan, and Viomi.

Sixty Months of Cartridges for Two Example Households

Five years is long enough for every RO cartridge in the table to come due at least once, since the longest RO rating among these systems is the Viomi M1's four years, so no design looks cheaper simply because its membrane change falls outside the window. The count follows three rules. The first set of cartridges ships installed and is not counted. The Viomi rows count each cartridge at its listed rated months in both examples, with the Viomi M1 at its maximum of 24 and 48 months. A replacement is counted when its due date falls inside the 60 months; one that falls exactly at month 60 belongs to year six. Each cartridge is counted on the replacement rule shown for it in the price table.

Two example households set the use level. The light-use example draws 1 gallon a day from the RO faucet, or 1,826 gallons over five years. The heavy-use example draws 4 gallons a day, or 7,304 gallons.

Totals are system price plus replacement cartridges. Drain water and electricity are worked out in the next section.

The cost-per-gallon column is also the easiest one to set beside what a household spends now. A family that buys bottled or refill water can divide its own monthly spending by the gallons it buys in a month and compare that figure with the column for its own use level.

Cartridge spending over five years falls between $339.94 and $419.94 for the four Viomi systems. The Viomi V8 PRO's cartridge spending lands below the Viomi V6 PRO's even with its pricier RO cartridge, because the spare pre-filter in its box covers the first change. The Viomi M1 reaches its total with only three cartridges, so its higher purchase price carries most of its five-year figure. Put in proportion, the purchase price is about 42% of the Viomi B6W's five-year total and about 72% of the Viomi M1's, which is why the two sit at opposite ends of the Viomi rows even though their cartridge spending is within about $10 of each other. On the two Waterdrop systems, the six-month CF pre-filter sets the pace: nine CF cartridges at light use, and thirteen once daily use passes the point where 550 gallons runs out before six months.

In these two examples, use moves cost per gallon a long way. Every system in the table costs less per gallon at 4 gallons a day than at 1, because the purchase price is spread over four times as much water. Once a system is installed, the cartridge line also keeps its own time: on the Viomi V6 PRO, Viomi V8 PRO and Viomi M1, remaining filter life shows on the faucet, so the next purchase on the worksheet is visible well before it is due.

The Drain Water and Electricity Lines

Drain water depends on the pure-to-drain ratio. A 3:1 system sends one gallon to the drain for every three it purifies, and a 2:1 system sends one for every two. In this worksheet, the Viomi V6 PRO, Viomi V8 PRO, Viomi M1 and G3P800 are rated at 3:1, and the Viomi B6W and G3P600 at 2:1. Over five years, that works out as follows for the two example households.

The example rate is $12 per 1,000 gallons of combined water and sewer charges. More on how drain ratios vary across RO designs is in this look at low-waste reverse osmosis brands.

Electricity for making water is smaller still. A tankless system draws its main power while it makes water, so the line uses two rated figures: the system's rated wattage and the hourly output, which is the GPD rating divided by 24. A 600 GPD rating works out to 25 gallons an hour, so the heavy-use example's 7,304 gallons take about 292 hours. At the Viomi V6 PRO's rated 68 watts, that comes to roughly 20 kWh over five years, or about $3.38 at the example rate of $0.17 per kWh. The other three Viomi systems land between about 15 and 32 kWh on the same steps, with the top of that range, roughly $5.36, belonging to the 1000 GPD Viomi M1. Both utility lines are rated-basis estimates.

Adding the lines in this worksheet for one system shows the proportions. For the Viomi V6 PRO in the heavy-use example, $799.93 for the system and cartridges, $29.22 for extra drain water and about $3.38 for water-making electricity add up to roughly $832.53 over five years, or about $0.11 for each of the 7,304 gallons. The purchase price and cartridges make up about 96% of that figure.

FAQ

Should a sale price go into the worksheet?

For a household's own purchase, the price it actually pays is the right number for the purchase line. The regular price is used here so that systems priced on different days, or during different promotions, can be compared on the same footing.

Why does the Viomi V8 PRO column buy one fewer PCB filter?

The Viomi V8 PRO ships with two PCB cartridges, one installed and one spare. The spare covers the first pre-filter change at month 12, so only the changes at months 24, 36 and 48 need a purchase.

Do the cartridges that come with the system count as replacements?

They are part of the purchase price. The count starts with the first cartridge a household has to buy, which is why the Viomi M1, counted at its rated months with the first change at month 24, buys two PCB cartridges and one RO cartridge inside five years in this worksheet.

How does the worksheet change for a three-year view?

The same count simply stops at month 36. Scaling the five-year total down by a fraction would misplace purchases that arrive in steps, such as an RO cartridge bought at month 24, so each cartridge is counted again inside the shorter window instead.

What happens to a cartridge that comes due exactly at month 60?

It goes into year six. A change at month 60 buys filtration for the months after the five-year window, so counting it would charge the first five years for water they never used. The same cut-off applies to a shorter window, such as a cartridge due at month 36 in a three-year view.

Reading Your Finished Worksheet

For the four Viomi systems, extra drain water and water-making electricity stay under $50 over five years in both examples at the example rates, even at 4 gallons a day. On a finished worksheet, the purchase price and the cartridge line therefore account for nearly all of the total, and the cartridge line depends on how many cartridges a design uses and how long each is rated to last.