The machine price is the number people compare. It is almost never the number that decides. Here is the arithmetic, with every assumption on the table.
For a three-person household over five years, filtered drinking water costs roughly 29 to 90 cents per gallon, depending on the system. Bottled water at typical US jug prices costs about $1.50 per gallon. The municipal water itself costs about half a cent.
The surprise is not that filters beat bottled water — that is obvious. The surprise is that the $35 pitcher is the most expensive filtered water on the page: its certified filter life is 15 gallons and a replacement costs $13–18, so a three-person household spends roughly $580 a year on cartridges. The $449 countertop machine, which looks extravagant on the shelf, makes the cheapest water here from year two onwards.
No hidden model. Four inputs, one division:
gallons per year = people × 0.6 gal/day × 365
total cost = upfront + (filters/year + electricity/year) × years
cost per gallon = total cost ÷ (gallons per year × years)
The 0.6 gallons per person per day covers drinking and cooking — not showering, laundry or the garden. For three people that is 657 gallons a year, or 3,285 gallons over five years. If your household differs, the calculator takes your own numbers.
| Option | Upfront | Per year | 5-year total | Cost / gallon |
|---|---|---|---|---|
| ZeroWater 10-cup pitcher | $35 | $584 | $2,955 | $0.900 |
| AquaTru countertop RO | $449 | $100 | $949 | $0.289 |
| Waterdrop G3P800 under-sink RO | $759 | $170 | $1,609 | $0.490 |
| Bottled water (1-gal jugs @ $1.50) | $0 | $986 | $4,928 | $1.500 |
| Municipal tap water, untreated | $0 | ≈$3 | ≈$16 | ≈$0.005 |
The tap-water line is an order-of-magnitude figure: most US utilities charge somewhere between $2 and $8 per thousand gallons, so drinking water costs a household a few dollars a year. Whatever you spend beyond that is the price of treatment, not of water.
Split each five-year total into hardware and consumables and the picture inverts:
| Option | Hardware | Filters & power | Filters as % of total |
|---|---|---|---|
| ZeroWater pitcher | $35 | $2,920 | 99% |
| AquaTru countertop RO | $449 | $500 | 53% |
| Waterdrop G3P800 | $759 | $850 | 53% |
The pitcher is the clearest case. Its certified filter life is 15 gallons. A three-person household drinks through roughly 44 filters a year, at $13 to $18 each depending on the pack. The $35 sticker buys you the jug; the water is on a subscription of about $580 a year that you did not sign.
| Option | 1 year | 5 years | 10 years |
|---|---|---|---|
| ZeroWater pitcher | $0.942 | $0.900 | $0.894 |
| AquaTru countertop RO | $0.836 | $0.289 | $0.221 |
| Waterdrop G3P800 | $1.414 | $0.490 | $0.374 |
Even in year one the pitcher does not win: the countertop system is already cheaper per gallon, and by year ten it is the cheapest water on the page by a wide margin. The pitcher only makes sense if you drink far less than 0.6 gallons a day per person, or if your water is low in dissolved solids and a filter genuinely lasts longer than its certified 15 gallons. If this is your home, the arithmetic points to a machine — provided it lasts, which is the assumption doing the most work in that last column.
A cheap gallon of the wrong treatment is not a bargain. What each option is independently certified to reduce — not what the box says:
Waterdrop sells the G3P800 as a bare unit and as bundles. Their affiliate catalogue pushes the bundles: one with an alkaline filter at $1,028.99, one with two years of filters at $1,318.93 (checked 7 Aug 2026). The bundles pay us several times what the bare unit pays, because commission is a percentage of a much larger basket.
So here is the sum, last rechecked live on 2 September 2026. The bare unit is $759 (list $999, shown as a $240-off promotion; on 11 August it was $849 with a $150 checkout code). Filters, as checked 11 August: the one-year combo is $89.97, the two-year combo $309.93 (≈$155 a year), and the loose parts for two years add up to $319.93. Unit plus two-year combo at these prices: $1,068.93.
We have withdrawn our 7 August conclusion that the two-year bundle cost "roughly $640 more". Two reasons, both ours to own: the prices it rested on no longer hold, and re-deriving it exposed a slip — it compared the bundle against filters alone, without the unit. The principle it illustrated still stands: bundles pay us several times the commission of a bare unit, prices move weekly, and the only sum that matters is the one you run on the day you buy. That is what the two buttons below are for.
Replacement filters — check today's price → Check the unit price yourself →
Affiliate links — we may earn a commission at no extra cost to you. Unit price verified 2 Sep 2026, filter prices 11 Aug 2026, and they move; the two buttons above exist so you can redo this sum with today's numbers rather than trusting ours.
Consumption of 0.6 gallons per person per day for drinking and cooking is a planning assumption, at the higher end of typical guidance, chosen so the running costs are not understated. Hardware and filter prices are US list prices checked August–September 2026 and will drift. Electricity is estimated at $10–15 a year for units with a pump; it is the least certain figure here and also the smallest.
Corrected 5 September 2026 (two errors, both ours): (1) the pitcher's filter cost was carried as $180 a year, which implied about $4 per filter — no such price exists; at the 12-pack list price of $13.33 per filter and the certified 15-gallon life it is about $584 a year, which moves the pitcher from cheapest to most expensive per gallon and reverses this page's earlier headline. (2) The horizon table still carried the Waterdrop unit's earlier $849 price, and its rows left out the $15 a year of electricity the calculator includes. Every table now uses the calculator's basis. The intro range moved from "28 to 42 cents" to "29 to 90 cents".
Certification data comes from the certifiers, not from retailers: NSF certified drinking-water treatment units, IAPMO R&T listings, and the WQA. General guidance from the CDC and the EPA.
Some links on this site are affiliate links; options shown without a link earn us nothing. We do not rank by commission: on this page the cheapest water (the countertop unit) is the one option we have no link for and earn nothing from.
Run the numbers for your own household →