Under-sink reverse osmosis runs $300–$950 installed and is the common case; this calculator's whole-house option can reach $2,300–$4,800 once labor, well-water surcharges and location are stacked in. That ceiling is worth flagging directly: this page's own cost table advertises whole-house RO up to $8,000, a figure the calculator itself cannot actually produce from any combination of its inputs.
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.
The whole-house ceiling this calculator can't actually reach
Run every input to its maximum — premium whole-house unit ($1,800–$3,500), high-cost location labor ($400–$800 × 1.25 = $500–$1,000), and a hard-well surcharge ($300) — and the highest total this calculator can output is $4,800. This page's own cost table lists whole-house RO at "$4,800–$8,000," a range that starts exactly where the calculator's own maximum output ends and continues to a figure the tool has no combination of inputs that reaches. If you're pricing whole-house RO, treat the $8,000 ceiling on the table as aspirational rather than something this calculator will ever actually show you.
There is a second gap worth knowing about: this page's cost table lists a "Multi-stage / premium under-sink" tier ($500–$1,500), but the calculator's own system-type options are under-sink, countertop, whole-house and tankless — there is no "multi-stage" system type to select. The under-sink premium tier ($550–$900 unit) is the closest match, but it is not the same line item as the table's multi-stage figure.
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 ceiling and multi-stage gap above were computed directly by running the module's own inputs to their stated maximums and comparing the result to this page's cost table. Wage figures are BLS OEWS May 2025. No figure is estimated or interpolated.