Inside the system

Three filters, one great glass of water.

Every Sentry H2O drinking system runs your water through a sequence of purpose-built stages. Each filter does one job well — one takes the bad out, one puts the good back, and one adds a barrier for wells. Here's exactly what each does, and when to change it.

Find my system See the Wellness System

1ToxyGuardtakes the toxins out
2AlkaGuardadds the minerals back
3BioChemGuardoptional bacteria & virus barrier

The three filters

What each one actually does

Stage 1 · the workhorse

ToxyGuard

Catalytic carbon + reduction media

A halved coconut resting above a pile of dark activated-carbon granules — ToxyGuard's catalytic carbon media is derived from coconut shells.

The toxin filter. Water hits ToxyGuard first, where a powerful blend of catalytic-carbon and reduction media adsorbs the chemistry city treatment and old pipes leave behind — a salt-free scale-control process softens it, and an oxygenation stage adds oxygen back.

What it handles

Chlorine & chloramine
Trihalomethanes (THMs)
Hydrogen sulfide (odor)
Lead, arsenic & mercury
Fluoride
Sediment to 1 micron
Scale — salt-free softening
Oxygenation — adds oxygen back

Its scale-control process converts hardness minerals into harmless crystals — softening without salt, chemicals or a regeneration cycle — and it re-oxygenates the water so it tastes alive rather than flat. In the independent under-sink lab test, most PFAS compounds treated by the system reached non-detect (97.4–99.9% where both values were quantified).

Replace about once a year

Stage 2 · the mineralizer

AlkaGuard

Mineral enrichment, not stripping

The good-taste filter. Where reverse osmosis strips water down to almost nothing, AlkaGuard is designed to release magnesium and calcium back into the water and gently raise the pH — neutralizing acidity and softening without salt as it goes.

What it handles

Adds calcium & magnesium
Gently raises pH
Neutralizes acidity
Salt-free softening
Rounder, smoother taste

Lab-tested 6.83 → 8.21 pH on the under-sink system — the minerals reverse osmosis removes are kept in. Its media also carries broad adsorption of VOCs, chloramines and taste-and-odor compounds while it re-mineralizes. A taste-and-mineral difference, not a health claim.

Replace about once a year

Optional Stage 3 · wells & extra margin

BioChemGuard

NASA-derived submicron barrier

The peace-of-mind filter. Added on the TriGuard (well) configuration and the Premium portable set, BioChemGuard uses NASA-derived electropositive attraction to trap particles far smaller than its own pores.

What it handles

Bacteria
Pathogen-based viruses
Cysts — ≥99.98%
Chlorine & iodine
Submicron particles to 0.2 micron

The manufacturer's media reduces cysts by at least 99.98% and captures submicron particles conventional filters miss — the right call for wells, homes near farmland, after flooding, or anyone who wants the extra margin. Pair it with a whole-home UV stage when living microbes are the concern.

Replace about once a year

And for wells — a fourth media

WellGuard

Advanced oxidation + selective ion-trapping · whole-home well tank

The three filters above are the under-sink drinking cartridges. Well water needs more, so the whole-home well system runs on a different media in its tank: WellGuard oxidizes and filters heavy metals, hydrogen sulfide and organics down to 3 microns, and selectively adsorbs nitrates with proprietary, regenerable ion-trapping beads. That's the media behind our custom-fitted, test-matched nitrate treatment — targeted removal without reverse osmosis's waste stream or stripped minerals.

What it targets

Iron & manganese
Nitrates (selective ion-trapping)
Arsenic
Radium & uranium
Hydrogen sulfide (rotten-egg odor)
Heavy metals — zinc, copper, lead
Sediment & turbidity to 3 microns

Built to your water See the well whole-home system Every well order includes a pre-ship water test

Which set is mine?

Your water decides the set

The under-sink Wellness System ships in two configurations. Same housing — the filters inside are the difference.

DualGuard

City water

ToxyGuard + AlkaGuard

Two filters for municipal, chlorinated supply — takes the chlorine, chloramine, PFAS, lead and arsenic out, then adds minerals back for great-tasting water.

Shop the Wellness System

TriGuard

Well & extra margin

ToxyGuard + AlkaGuard + BioChemGuard

Adds the third BioChemGuard stage for bacteria, viruses and cysts — the right choice for wells, homes near farmland, or after flooding.

Choose TriGuard

Whole-home systems treat every tap and are configured differently — including nitrate-selective media matched to your water test where nitrates are a concern. See whole home →

Keeping it fresh

When to replace each filter

Under-sink drinking filters

Once a year

DualGuard or TriGuard sets are a yearly swap. Subscribe & save 15% and we auto-ship the exact set with a reminder — skip or cancel anytime.

Shop replacement filters

Whole-home tank media

Every 1–7 years

The tank media is refreshed — not replaced — with the Whole Home Revitalizer: every 1–3 years on city systems, 5–7 years on well systems, by household size.

See the Revitalizer

Portable filter sets

About a year

Standard (city) or Premium BioChemGuard (well / off-grid) sets swap yearly. Subscribe so you're never caught without on the road.

Shop portable filters

Filter life varies with your water quality and how much you use. A filter-life estimate for your home is on the filter-life estimator.

Beyond your glass

Every filtered glass is a bottle that never gets made.

single-use bottles a family of four can skip every year with filtered water on tap.

Shop whole home See the honest comparison

of all plastic ever made has been recycled

OECD, 2022

~80%

still sits in a landfill or the environment

Science Advances, 2017

plastic bottles bought every minute, worldwide

Euromonitor / The Guardian

Bottle count estimated from ~156–167 bottles per person a year (industry compilations) — yours depends on what you buy today. Plastic figures describe global plastic waste broadly; sources on file.

Straight answers

Filter questions

How often do the drinking filters need changing? +

The under-sink drinking filters — ToxyGuard, AlkaGuard and (on TriGuard) BioChemGuard — are a once-a-year swap. Subscribe to auto-ship and we send the exact set on schedule with a reminder before you run low.

What is the difference between DualGuard and TriGuard? +

DualGuard is the 2-filter set for city water: ToxyGuard + AlkaGuard. TriGuard adds a third BioChemGuard stage — a NASA-derived submicron barrier that reduces bacteria, viruses and cysts (by at least 99.98%) — the right choice for wells, homes near farmland, or anyone who wants the extra margin.

Do these filters waste water like reverse osmosis? +

No. There is no drain line and no wastewater. A typical reverse-osmosis system sends 3 to 5 gallons down the drain for every gallon it makes; the Sentry H2O stages send none — and AlkaGuard keeps the minerals RO strips out.

What about nitrates? +

Nitrates are handled at the whole-home level, where the system is custom-fitted with nitrate-selective media matched to your water test — targeted nitrate removal without reverse osmosis's waste stream or stripped minerals.

Are these tested by a lab? +

Yes. Sentry H2O reports its systems are tested to NSF standards; certification documents are being finalized, so we do not call them NSF certified. The independent before-and-after lab reports on our Science page are third-party testing, not a certification.

Real customers, real water

Real homes, real water

Verified Sentry H2O reviews — the same filters, in real kitchens.

Verified reviews of Sentry H2O systems, independently collected by Judge.me.

4.92 /5 ★★★★★

Based on 457 reviews 91% Verified

5 434

4 14

3 7

2 0

1 2

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