10 models to compare

Reverse osmosis systems: which need tank space?

Only APEC's two need tanks. ROES-50 and RO-90 rate 50 and 90 GPD; Waterdrop's eight tankless systems rate 400-1,600 GPD.

G3P800, X12 and X16 rate 3:1 pure-to-drain; X8-A matches G3P800's 800 GPD at 2:1.

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With no preferences selected: RO-90 Under-Sink Reverse Osmosis System is one option to compare.

No hands-on testingMethod and sources

RO-90 Under-Sink Reverse Osmosis System · first with a product link

Rated daily output: 90 gal/day.
Maker-described stages: 5.

What to note:

Not listed by the maker: pure-to-drain ratio.

View at APEC

If you choose Tankless for tank layout, the first option with a product link becomes G2 Reverse Osmosis System.

10 models compared; 10 have a product-page link.

The picks

5 options to compare

Compare the details that matter to your setup.

An option to compare

RO-90 Under-Sink Reverse Osmosis System

Rated daily output: 90 gal/day.

Key details

Maker-described stages: 5.

What to note

Not listed by the maker: pure-to-drain ratio.

Compare specs: Rated daily output: 90 gal/day here; 50 gal/day on ROES-50 Under-Sink Reverse Osmosis System.

Tank layout: Storage tankRated daily output: 90 gal/dayMaker-described stages: 5

See all 4 specs

Tank layoutStorage tank

Rated daily output90 gal/day

Maker-described stages5

Pure-to-drain ratioNot listed by the maker

3 of 4 specs available · source checked September 26, 2026 · Source ↗
APEC · Product page checked September 26, 2026

View at APEC Compare

Tank layout: Tankless

G2 Reverse Osmosis System

Tank layout: Tankless.

Key details

Rated daily output: 400 gal/day.

What to note

Not listed by the maker: pure-to-drain ratio.

Compare specs: Tank layout: Tankless here; Storage tank on RO-90 Under-Sink Reverse Osmosis System.

Tank layout: TanklessRated daily output: 400 gal/dayMaker-described stages: 7

See all 4 specs

Tank layoutTankless

Rated daily output400 gal/day

Maker-described stages7

Pure-to-drain ratioNot listed by the maker

3 of 4 specs available · source checked September 26, 2026 · Source ↗
Waterdrop · Product page checked September 26, 2026

View at Waterdrop Compare

Rated daily output: 50 gal/day

ROES-50 Under-Sink Reverse Osmosis System

Tank layout: Storage tank.

Key details

Rated daily output: 50 gal/day.

What to note

Not listed by the maker: pure-to-drain ratio.

Compare specs: Tank layout: Storage tank here; Tankless on T4-A Reverse Osmosis System.

Tank layout: Storage tankRated daily output: 50 gal/dayMaker-described stages: 5

See all 4 specs

Tank layoutStorage tank

Rated daily output50 gal/day

Maker-described stages5

Pure-to-drain ratioNot listed by the maker

3 of 4 specs available · source checked September 26, 2026 · Source ↗
APEC · Product page checked September 26, 2026

View at APEC Compare

Maker-described stages: 8

G3P600 Reverse Osmosis System

Rated daily output: 600 gal/day.

Key details

Tank layout: Tankless.

What to note

Maker-described stages: 8.

Compare specs: Rated daily output: 600 gal/day here; 90 gal/day on RO-90 Under-Sink Reverse Osmosis System.

Tank layout: TanklessRated daily output: 600 gal/dayMaker-described stages: 8

See all 4 specs

Tank layoutTankless

Rated daily output600 gal/day

Maker-described stages8

Pure-to-drain ratio2:1

4 of 4 specs available · source checked September 26, 2026 · Source ↗
Waterdrop · Product page checked September 26, 2026

View at Waterdrop Compare

Also compare 5

G3P800 Reverse Osmosis System

Rated daily output: 800 gal/day.

Key details

Tank layout: Tankless.

What to note

Maker-described stages: 10.

Compare specs: Rated daily output: 800 gal/day here; 90 gal/day on RO-90 Under-Sink Reverse Osmosis System.

Tank layout: TanklessRated daily output: 800 gal/dayMaker-described stages: 10

See all 4 specs

Tank layoutTankless

Rated daily output800 gal/day

Maker-described stages10

Pure-to-drain ratio3:1

4 of 4 specs available · source checked September 26, 2026 · Source ↗
Waterdrop · Product page checked September 26, 2026

View at Waterdrop Compare

Comparing RO-90 Under-Sink Reverse Osmosis System · ROES-50 Under-Sink Reverse Osmosis System

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The facts that differ

Choose up to three models to compare side by side.

Differences only

2 identical specs shown. Details that do not apply to these models are omitted.

Published specification comparison
Spec	RO-90 Under-Sink Reverse Osmosis SystemNo preferences selected.	ROES-50 Under-Sink Reverse Osmosis SystemNo preferences selected.
Tank layout	Storage tank	Storage tank
Rated daily output	90 gal/day	50 gal/day
Maker-described stages	5	5

RO-90 Under-Sink Reverse Osmosis System

No preferences selected.

Tank layout: Storage tank
Rated daily output: 90 gal/day
Maker-described stages: 5

ROES-50 Under-Sink Reverse Osmosis System

No preferences selected.

Tank layout: Storage tank
Rated daily output: 50 gal/day
Maker-described stages: 5

RO-90 Under-Sink Reverse Osmosis System

View at APEC

ROES-50 Under-Sink Reverse Osmosis System

View at APEC

Compare all 10 models

— = no verified listing yet. The published order is independent of links.

All models and their decision specs
Product	How it compares	Key spec	Compare	Action
RO-90 Under-Sink Reverse Osmosis System	Compared with ROES-50 Under-Sink Reverse Osmosis System: rated daily output, 90 gal/day vs 50 gal/day.	Tank layout: Storage tank	Compare	View at APEC
ROES-50 Under-Sink Reverse Osmosis System	Compared with T4-A Reverse Osmosis System: tank layout, Storage tank vs Tankless.	Tank layout: Storage tank	Compare	View at APEC
G2 Reverse Osmosis System	Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.	Tank layout: Tankless	Compare	View at Waterdrop
G3P600 Reverse Osmosis System	Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.	Tank layout: Tankless	Compare	View at Waterdrop
G3P800 Reverse Osmosis System	Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.	Tank layout: Tankless	Compare	View at Waterdrop
K6 Reverse Osmosis System	Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.	Tank layout: Tankless	Compare	View at Waterdrop
T4-A Reverse Osmosis System	Compared with X8-A Reverse Osmosis System: rated daily output, 450 gal/day vs 800 gal/day.	Tank layout: Tankless	Compare	View at Waterdrop
X8-A Reverse Osmosis System	Maker-described stages: 10; Tank layout: Tankless.	Tank layout: Tankless	Compare	View at Waterdrop
X12 Reverse Osmosis System	Compared with X8-A Reverse Osmosis System: rated daily output, 1,200 gal/day vs 800 gal/day.	Tank layout: Tankless	Compare	View at Waterdrop
X16 Reverse Osmosis System	Compared with X8-A Reverse Osmosis System: rated daily output, 1,600 gal/day vs 800 gal/day.	Tank layout: Tankless	Compare	View at Waterdrop

RO-90 Under-Sink Reverse Osmosis System

Compared with ROES-50 Under-Sink Reverse Osmosis System: rated daily output, 90 gal/day vs 50 gal/day.

Tank layout: Storage tank

CompareView at APEC

ROES-50 Under-Sink Reverse Osmosis System

Compared with T4-A Reverse Osmosis System: tank layout, Storage tank vs Tankless.

Tank layout: Storage tank

CompareView at APEC

G2 Reverse Osmosis System

Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.

Tank layout: Tankless

CompareView at Waterdrop

G3P600 Reverse Osmosis System

Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.

Tank layout: Tankless

CompareView at Waterdrop

G3P800 Reverse Osmosis System

Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.

Tank layout: Tankless

CompareView at Waterdrop

K6 Reverse Osmosis System

Compared with RO-90 Under-Sink Reverse Osmosis System: tank layout, Tankless vs Storage tank.

Tank layout: Tankless

CompareView at Waterdrop

T4-A Reverse Osmosis System

Compared with X8-A Reverse Osmosis System: rated daily output, 450 gal/day vs 800 gal/day.

Tank layout: Tankless

CompareView at Waterdrop

10 catalog models

How the comparison works

Your choices are compared with each model’s product details. A missing or conflicting value stays unknown and cannot satisfy a choice you select. The starting order helps you browse; it does not rate real-world performance.

Source dates appear with each link below. A source date does not confirm today's price or stock.

Finder methodology Report a correction

Sources for all 10 models

G2 Reverse Osmosis System: Source 1 ↗ · September 26, 2026
G3P600 Reverse Osmosis System: Source 1 ↗ · September 26, 2026
G3P800 Reverse Osmosis System: Source 1 ↗ · September 26, 2026
K6 Reverse Osmosis System: Source 1 ↗ · September 26, 2026
RO-90 Under-Sink Reverse Osmosis System: Source 1 ↗ · September 26, 2026
ROES-50 Under-Sink Reverse Osmosis System: Source 1 ↗ · September 26, 2026
T4-A Reverse Osmosis System: Source 1 ↗ · September 26, 2026
X12 Reverse Osmosis System: Source 1 ↗ · September 26, 2026
X16 Reverse Osmosis System: Source 1 ↗ · September 26, 2026
X8-A Reverse Osmosis System: Source 1 ↗ · September 26, 2026

Tank layout comes before the daily-production figure

APEC's storage-tank systems have maker production ratings of 50 and 90 gallons per day. Waterdrop's systems here are tankless, with daily ratings reaching 1600 gallons per day. Those ratings describe production under maker conditions, not faucet flow or household consumption.

Check cabinet dimensions, supply pressure and power arrangements for the exact system. No faucet-flow measurements were taken; Waterdrop and APEC documentation supplies the system details here. Tankless versus storage tank is an installation choice; a larger daily rating cannot settle cabinet fit or contaminant reduction.

Stages and drain ratios are different kinds of claims

The makers' stage counts range from 5 to 11. APEC's storage-tank systems use a 5-stage description, while Waterdrop's tankless systems have different stage counts. A stage is maker terminology, not a cartridge count or evidence that a particular contaminant is reduced.

Some Waterdrop systems claim pure-to-drain ratios, but missing or conflicting ratios stay unknown. Read model-specific performance data, replacement-cartridge details and installation instructions together. Maintenance schedules and treatment for your water remain unanswered by stage count and daily-production ratings.

Before you buy

Does a higher GPD rating mean more water at the faucet?

Not necessarily. GPD is each maker's daily production rating, not faucet flow or what your household uses, and APEC and Waterdrop each rate their own systems. APEC's two systems come with a 4 gallon tank.

Do more filtration stages mean cleaner water?

Stage counts are each maker's own description, from 5 to 11, and they don't measure contaminant removal or tell you how many cartridges you'll replace. Waterdrop's K6, which it titles an instant hot water dispenser, is rated 600 GPD with 5 stages, and the T4-A 450 GPD with 10. For removal claims, go to each model's performance data.

What should I sort out before installing one?

Cabinet space, water pressure and power needs aren't compared here, so read the model's installation guide first, and hire a plumber if you aren't comfortable making the water-line connections. The G2 and both APEC pages give no drain ratio.