Most homes don't need the most expensive system. Answer a few questions and see whether you need treatment at all — and if so, which certified options fit your documented problem — with the real cost of each, side by side, so the long-term price is your call, not ours.
Mae: Before you buy a filter, read your free water report. Many homes don't need one.
Already decided on an under-sink reverse-osmosis system? The one we'd start with: Waterdrop G3P800 — check what it is certified for in the details below before you buy.
Not sure yet? The 6 questions below may tell you to buy nothing. Plain link: we earn nothing if you buy.
Your water, in 6 questions
There are no wrong answers, and "you don't need anything" is a real result. Pick "I don't know" whenever that's the honest answer.
The kitchen-table math: a house of 7
Our "Ask Matt & Mae" episode used the older ZeroWater-branded filter (15 gallons, $13.33: $1,363 a year). This page uses the Culligan-branded pitcher on the IAPMO listing, with its own 20-gallon filter at $14.50. Corrected 21 October 2026 after an independent review. Change the calculator above for your own house.
Matt7 of us × 0.23 gallons a day × 365 = 587 gallons a year to drink and cook. That's the EPA's average, not a guess.
MaeAnd our lead-certified pitcher?
Matt20 gallons per filter → 587 ÷ 20 = 29.3 filters × $14.50 = $425 a year.
DavidUnder the sink, certified for lead too: $849 once. At our volume the filters run on the calendar (CF every 6 months, CB every 12, membrane every 24): with power and drain water, about $178 a year. It pays back against that pitcher in about 3.4 years.
MaeSo we keep $247 a year against that pitcher. But a lead-certified faucet filter is about $82 a year, with nothing to install under the sink.
IvyRead the water report first. If it says "fine" and the house has no old lead pipes, we might not need a filter at all.
A dinner out every few months
A start on a college fund
Or less to worry about
Why lead is the number to check
There is no known safe level of lead in the body. Young children are most at risk: lead can lower IQ and harm attention and behaviour. In adults it is linked to higher blood pressure.
A pooled study of 1,333 children in seven cohorts found the steepest IQ loss at the lowest exposures: 3.9 IQ points as blood lead rose from 2.4 to 10 µg/dL [11]. In Flint, Michigan, the share of young children with elevated blood lead roughly doubled, from 2.4% to 4.9%, after the city changed its water source [12].
The EPA estimates up to 9 million lead service lines, the pipes from the water main under the street into a home, are still in use [9].
What a certificate means: to be certified for lead under NSF/ANSI 53, a filter must cut test water from 150 to 5 parts per billion [4]. Look for the standard and the word "lead" on the listing, not the box.
Most water reports say the water is fine. Yours is free and comes every year [8]. If it shows lead, choose a lead-certified filter. If it doesn't, you may need nothing.
Same 587 gallons a year for 7 people (EPA average use), bought in 16.9 oz bottles.
≈ 4,400plastic bottles a year
≈ 370a month to rinse, crush, bag and take to the curb
≈ 94 lbof water carried in from the car, every week (8.34 lb a gallon)
≈ $13a year in trash bags (estimate: 55–75 kitchen bags)
One extra store run a week, at the IRS rate for the full cost of driving (72.5¢ a mile, 2026) [13]:
Per year
$226
Fuel alone is about a quarter of that at today's $4.33 a gallon national average [14].
What we read for this page
New:the evidence library holds all 108 studies and official sources we read, sorted by theme. Each one has its numbers quoted, its limits stated and an evidence grade.
20 documents, including 2 peer-reviewed studies (14 journal pages). Checked 16 October 2026.
Lanphear BP et al. Low-level environmental lead exposure and children's intellectual function: an international pooled analysis. Environmental Health Perspectives 113(7):894–899, 2005. Peer-reviewed.Full text
Hanna-Attisha M et al. Elevated blood lead levels in children associated with the Flint drinking water crisis. American Journal of Public Health 106:283–290, 2016. Peer-reviewed.Record
We follow the public guidance, not marketing copy:
CDC — Choosing a home water filter: not every home needs a filter; different filters remove different things; many standard filters don't remove germs; poor maintenance can cause problems; point-of-use makes sense when only drinking/cooking water needs treating. cdc.gov
EPA — Home drinking water filtration fact sheet.epa.gov
NSF — Home water treatment & certification. Match the contaminant to the right NSF/ANSI standard (42 = taste/chlorine; 53 = lead & health effects; 58 = reverse osmosis; 401 = emerging contaminants incl. some PFAS; 44 = softeners). nsf.org · verify a product
How we choose — and what we won't do
We only suggest a product for a specific contaminant if it's independently certified for that contaminant. If we don't have a certified match, we say so and point you to the NSF listings — we don't guess.
We never say "removes toxins" or "healthier water" as a blanket claim. Certifications name specific substances and reduction levels; that's what we cite (and ask you to verify).
"No treatment needed" and "test first" are real, common results — not failed sales.
Costs are estimates; you can edit the key ones. Where a figure is uncertain (electricity, reject-water) we show it as a rough estimate, not false precision.
Some options below are candidates without a purchase link because we haven't joined that affiliate program yet — they're shown for completeness, not profit.
Part of Do Your Own Math
Four calculators, one rule: show the math
The Water Math is one of four independent tools. Same method, same honesty rules — no fear-selling, sources for every claim, and "you don't need to buy anything" is always an allowed answer.
What we are: a small independent project, published under a brand name rather than a person. We're anonymous by choice — but not unaccountable, which is what this page is for.
Desk-researched, not hands-on tested. This matters, so we'll say it plainly: we have not physically tested the products we point to. Our picks come from manufacturer specifications, independent certifications (NSF/ANSI, AHAM, IAPMO), published lab-style reviews and customer feedback at scale. Where we say a product is certified for something, we link you to the certifier's database — certification is model- and contaminant-specific, so check that the exact model is listed for the exact substance you care about before buying. If you want hands-on testing, read a site that does that — and then come back for the math.
How the numbers work: every calculator shows its assumptions and lets you change the ones that matter. Where published estimates disagree (they often do), we show the range rather than the flattering end, and we say which input is the least certain.
How we're funded: there are no affiliate links — no link on this site earns us anything. Options shown without a link earn us nothing; we include them when they're genuinely the right answer. We never rank by commission, and the highest-paying option is regularly not our first pick.
What we won't do: claim a product removes something it isn't certified for, invent urgency, use a fake live counter, gate useful information behind an email, or tell you to buy when the honest answer is "test first" or "you don't need this".
Mistakes: we get things wrong. When we do, we change the page rather than quietly delete it — recent corrections include replacing a single water figure with an honest range, removing a life-expectancy estimate that misapplied population research, and dropping a product we couldn't stand behind. If you spot an error, we'd rather know.
Not professional advice. These are planning estimates and general information, not medical, plumbing or safety advice.
Product details last checked: 2 August 2026. Prices and availability change — always confirm on the retailer's page before buying.
📍 New: what is in the water where you live
Type your ZIP code and see the PFAS and lithium results EPA measured at the water systems that serve it (UCMR 5, final dataset August 2026): 10,313 systems, 20,768 ZIP codes, compared with the 2024 limits. Nothing you type leaves your browser.
A $35 pitcher and a $449 countertop system land within four cents of each other over five years — because filters, not machines, drive the cost. Full worked tables, every assumption shown.
Every product on this page, checked against what NSF, IAPMO and the WQA actually list — the standard numbers, the reduction figures, and the gaps. One of our picks turned out to hold no certification at all for the thing we were recommending it for, so we changed the recommendation.
