Under-sink reverse osmosis runs $300–$950 installed and is the common case. The calculator's whole-house path returns the published installed range of $4,800–$8,000 on city water, and $5,100–$8,300 with a hard-well pretreatment surcharge; brand tier and local labor rate do not move it, because the source publishes one installed range rather than a unit and labor split.
How this calculator builds the installed price
Each system type has its own unit-cost and labor bands by brand tier — budget, midrange or premium — and labor is further scaled by a location multiplier (low-cost 0.85x, average 1.0x, high-cost 1.25x). Well water adds a flat surcharge on top: $150 for a standard well, $300 for hard well water that needs pre-treatment.
Switch that same job to a well with hard water in a high-cost location and the labor band alone moves to $125–$250 (×1.25), plus a $300 surcharge — pushing the total to $725–$1,100 for the identical unit.
How the whole-house path is priced, and what moves it
The whole-house path does not build its price from unit and labor rows. It returns the dataset's published installed range for whole-house reverse osmosis (Angi, retrieved 2026-07-13), the same $4,800–$8,000 this page's cost table shows. At the default inputs (city water, 5 gallons a day) the result is $4,800–$8,000. Switching to hard well water in a high-cost location adds only the $300 pretreatment surcharge and returns $5,100–$8,300, which is the highest total the calculator can output for this system.
Because the source gives one installed range, the brand-tier and labor-market inputs are ignored on this path; the breakdown row says so rather than implying a labor split was costed. Under-sink is different: at midrange on city water and average labor it returns $400–$750, and at the premium tier $700–$1,200, which sits inside the table's "Multi-stage / premium under-sink" band of $500–$1,500. The multi-stage row is the Under-Sink option at the Premium tier; there is no separate multi-stage system type to select.
What the cost-per-gallon figure actually compares
This calculator also returns a cost-per-gallon figure and a bottled-water comparison, both built from your stated daily usage. It amortizes the installed cost over five years, adds the system's annual filter-replacement cost (which ranges from $40/yr for a countertop unit to $150/yr for whole-house), and divides by the gallons produced in a year at your stated daily rate.
The bottled-water comparison uses a flat $1.50 per gallon assumption — this calculator's own baseline, not a sourced national bottled-water price — so treat it as a rough contrast rather than a market figure. What it does show reliably is the shape of the tradeoff: RO's cost per gallon falls as usage rises, because the fixed installed cost is spread across more gallons, while bottled water's per-gallon cost stays flat no matter how much you use.
Why labor still moves the price on a small plumbing job
Even a modest under-sink install is licensed plumbing work in most jurisdictions once it ties into a home's water supply and drain line. The Bureau of Labor Statistics puts plumbers' mean hourly wage at $34.70 nationally — the highest-paid trade among the systems calculators on this site — which is the real force behind this calculator's location multiplier, even on jobs where the unit itself costs less than a day of labor.
Whether reverse osmosis is the right answer
Reverse osmosis is a capable treatment method, and it is also frequently sold to solve problems it does not solve. The starting point is a water test rather than a system quote.
Test first, because the results determine the technology. Hardness is a softener problem, not an RO problem. Sediment wants filtration. Bacteriological contamination wants disinfection. RO addresses dissolved solids, and buying it for the wrong contaminant means paying for a system that leaves the actual issue in place.
There are real trade-offs to weigh even when RO is right. It produces wastewater alongside treated water, it needs cartridge and membrane replacement on a schedule, and it removes dissolved minerals indiscriminately, which changes how the water tastes to some people.
The under-sink versus whole-house decision usually turns on the same test result. If the concern is drinking water, treating one tap is far cheaper. Whole-house treatment is for problems that affect bathing, laundry and appliances — a different and larger scope.
Methodology
Unit, labor, water-surcharge and filter-cost bands are the literal constants in this calculator's module (src/lib/calculators/ro-installation.ts). The whole-house and under-sink ranges above are computed at render by running that module at the inputs named in the text; the whole-house range is read from the dataset (src/data/costs/ro-installation.ts, Angi, retrieved 2026-07-13) rather than typed. Wage figures are BLS OEWS May 2025. No figure is estimated or interpolated.
Sources
- U.S. Bureau of Labor Statistics — OEWS Profile, Plumbers, Pipefitters and Steamfitters (47-2152), May 2025 — accessed 2026-09-07
- Angi — Reverse Osmosis Water Filter Cost (2026) — accessed 2026-07-13