Bulk buying vs regular
Compare bulk warehouse packs with normal store sizes. Counts food waste, faster use at home, shelf space, and cash tied up.
5-year net savings
+$3,772
Home filter ($745) vs Bottled water ($4,517) over 5 yrsExample calculationYes, breaks even in 4 months and saves $3,772 over 5 years
At 1.5 gallons/day (548 gal/yr), a $260 home filter system with $97/yr in cartridges and tap water pays for itself in 4 months. You save $546 in year 1 and $3,772 over 5 years while avoiding 4,147 single-use 16.9 fl oz bottles per year.
5-year net savings
+$3,772
$745 filter vs $4,517 bottled (5 yrs)Year-1 net savings
+$546
4 months to recover $260 upfrontEffective cost per gallon
$0.27 vs $1.65
Filter vs bottled per gallon (5 yrs)Plastic bottles avoided
4,147/yr
20,735 16.9oz bottles over 5 yrsSide-by-side 5-year water cost breakdown
| Drinking water cost item | Bottled water | Home water filter |
|---|---|---|
| Upfront filter system / bottle cooler setup | $0 | $260 |
| Plumber or handyman installation | $0 | $0 |
| Bottled water cases or 5-gallon jugs (5 yrs) | $4,517 | $0 |
| Cooler rental & delivery fees (5 yrs) | $0 | $0 |
| Replacement filter cartridges & RO membranes (5 yrs) | $0 | $425 |
| Municipal tap & RO reject water (5 yrs) | $0 | $60 |
| Total 5-year drinking water cost | $4,517 | $745 |
| Effective cost per gallon (2,738 gallons) | $1.65/gal | $0.27/gal |
5-year cumulative cost and plastic bottle savings
See how fast recurring bottled water cases or 5-gallon deliveries overtake an under-sink filter:
| Horizon | Bottled water | Home water filter | Cumulative savings | 16.9oz bottles avoided |
|---|---|---|---|---|
| Year 1 | $903 | $357 | +$546 | 4,147 bottles |
| Year 2 | $1,807 | $454 | +$1,353 | 8,294 bottles |
| Year 3 | $2,710 | $551 | +$2,159 | 12,441 bottles |
| Year 4 | $3,614 | $648 | +$2,966 | 16,588 bottles |
| Year 5 | $4,517 | $745 | +$3,772 | 20,735 bottles |
How this calculator works
A typical 2-to-3-person household uses roughly 1.5 gallons of purified water per day for drinking, coffee, ice, and cooking (548 gallons per year). Buying that volume in supermarket 24-packs of 16.9 fl oz bottles at $1.65 per gallon costs about $903 every year and requires hauling more than 4,100 single-use plastic bottles home from the store.
Including replacement cartridges and RO reject water
Many filter calculators ignore ongoing consumables. This model includes both annual sediment/carbon pre-filter sets and reverse osmosis membrane replacements ($65 to $110 per year), plus the municipal water and sewer bill for the 3-to-1 reject water ratio of a standard under-sink RO system (typically $10 to $15 per year).
Frequently asked questions
How much does an under-sink reverse osmosis filter cost per gallon?
Including the $260 upfront system, $85 per year in replacement pre-filters and RO membranes, and $12 per year in municipal water and wastewater charges, a home RO system produces purified water for about $0.27 per gallon over five years, compared with $1.25 to $2.00 per gallon for bottled water.
Does reverse osmosis waste a lot of tap water?
A traditional tank-style RO system sends roughly 3 gallons of reject water down the drain for every 1 gallon of purified drinking water. However, because drinking water is a tiny fraction of household water use, 1.5 gallons/day of drinking water uses only about 2,200 gallons of total feed water per year, which costs roughly $12 per year at average U.S. water and sewer rates.
How many 16.9 oz bottles equal one gallon of water?
One U.S. liquid gallon is 128 fluid ounces, so 1 gallon equals 7.57 standard 16.9 fl oz (500 mL) water bottles. A household drinking 1.5 gallons per day avoids 4,147 plastic bottles per year.
Benchmark sources and dates
Starting assumptions are example benchmarks, not binding quotes. Change any input to match your own bills or offers.
| Assumption / Input | Starting value | Source | Checked |
|---|---|---|---|
| Under-sink reverse osmosis (RO) system purchase and annual replacement filter/membrane cost | $260 upfront DIY under-sink RO system + $85/yr replacement sediment, carbon, and RO membrane cartridges | NSF International Certified Drinking Water Treatment Units and Consumer Reports Water Filter Guide | 2026-04-01 |
| Municipal tap water and RO reject water utility cost | $12/yr municipal water and sewer volume for 1.5 gal/day product water (at 3:1 RO brine ratio) | U.S. Environmental Protection Agency WaterSense Indoor Water Use and Municipal Rate Benchmarks | 2026-04-01 |
| Retail bottled water price per gallon (cases of 16.9 fl oz bottles vs 5-gallon delivery) | $1.65/gallon for multi-pack 16.9 fl oz (500 mL) cases | U.S. Bureau of Labor Statistics Average Retail Food and Beverage Prices and IBWA Benchmarks | 2026-04-01 |
| Household daily drinking and cooking water consumption | 1.5 gallons/day (547.5 gallons/year, equivalent to 4,147 single-use 16.9 fl oz bottles/year) | Centers for Disease Control and Prevention (CDC) Plain Water Intake Benchmarks | 2026-04-01 |