Quick Answer: The Express Water RO5DX is a no-frills 5-stage under-sink RO: 50 GPD, a 4-gallon tank holding about 3.2 gallons, NSF certified, running on 40–80 psi with no electricity. The current Amazon listing sells it with a chrome faucet, a spare filter set and a leak detector, under a generic "5-Stage RO" title rather than the RO5DX name. It's a good fit for a household that drinks and cooks with a few gallons a day and especially for softened-water homes that want the sodium out of the kitchen tap. It's not the pick if your pressure sits under 40 psi, if you want added minerals, or if a fridge and ice maker will also draw from it. In those cases, look at the iSpring RCC7AK. The APEC ROES-50 is the closest like-for-like rival.
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Here's the situation most of our readers are in when they look at the RO5DX: the softener is in, the scale is gone, and now somebody in the house says the tap water tastes a bit flat or salty. Or someone on a low-sodium diet asks whether softened water is OK to drink. An under-sink RO is the standard answer, and the RO5DX is one of the plainest, most widely sold ones.
Plain isn't an insult here. Five stages, a tank and a faucet, with nothing to plug in. I haven't installed one. This review comes from Express Water's published specs and filter guidance, the Amazon listing, and retailer pages.
In this guide
What the five stages are
Express Water's replacement sets for its 5-stage systems include these cartridges, which line up with the RO5DX's stages:
- Sediment (SED): catches particles that would clog everything downstream
- Granular activated carbon (GAC): removes chlorine, which damages RO membranes
- Activated carbon block (ACB): a second, finer carbon pass
- RO membrane (50 GPD): does the real work on dissolved solids, including sodium
- Post carbon: a polishing stage for taste as water leaves the tank
The full published spec: 50 GPD output, a 4-gallon tank with 3.2 gallons of usable water, NSF certification (the current listing title says "NSF Certified" without naming standards; earlier RO5DX listings cited NSF/ANSI 58 for RO performance and 372 for lead-free materials), 40–80 psi operating pressure, no electricity, and a chrome faucet. The current listing also includes an extra filter set and a leak detector, and Express Water says everything needed to install it, except tools, is in the box.
Is 50 GPD enough? Usually, yes
"Gallons per day" sounds like a capacity limit, but it's a production rate under test conditions. What matters at the faucet is the tank.
Take a family of four drinking about half a gallon each and cooking with another gallon or so:
- Drinking: 4 x 0.5 = 2 gallons
- Cooking, coffee, pets: about 1–1.5 gallons
- Daily total: about 3–3.5 gallons
That roughly empties the 3.2-gallon tank once a day, and a 50 GPD membrane refills it overnight with plenty of margin even at lower real-world output. Where 50 GPD falls short is when you tie a fridge and ice maker in, fill big pots for canning, or have a large family. A pitcher-filling session drains the tank, and you're left waiting for the slow trickle of the membrane. That's when a 75 GPD unit with remineralization starts to make sense.
Pressure: the 40 psi floor matters
RO membranes run on pressure, and the RO5DX has no booster pump. Below 40 psi, production drops, the tank fills slowly, and more water goes to drain per gallon made.
Softener homes should check this. A softener and a whole house filter can each take a few psi off the line, and if you're on a well with a 30/50 pressure switch, you'll spend part of every cycle under 40. Our guide to low water pressure after a water softener shows how to measure it. If you're consistently under 40, pick a system with a pump instead.
The filter calendar
Express Water's guidance on its RO filter sets:
| Cartridge | Replace |
|---|---|
| Sediment, GAC, carbon block | Every 6 months |
| RO membrane and post carbon | Once a year |
That's conservative. On softened city water with little sediment, the prefilters often have life left at six months. Still, swapping the GAC on time protects the membrane from chlorine, and the membrane is the expensive part. Express Water sells multi-year filter sets, and the RO5DX is also listed on Amazon bundled with a 3-year set.
How do you know when the membrane is really done? A TDS meter tells you. Read the tap, read the RO faucet, and track the percentage removed over time. When it slips noticeably, the membrane is due. Our RO filter change guide walks through the full swap and the sanitizing step.
Softener plus RO: why the pairing works
Ion exchange swaps hardness for sodium. In most homes that's a small amount, but it rises with your hardness. Our explainer on sodium in softened water works out the numbers. An RO membrane removes most of that sodium, along with the hardness the softener already took out. And soft feed water means less scale on the membrane, so it lasts longer than it would on hard water.
That's why softener-then-RO is such a common setup, rather than plumbing the kitchen cold line around the softener. We cover both options in reverse osmosis and a water softener together and should a kitchen tap bypass the softener.
What Express Water doesn't tell you on the listing
- Waste ratio. Every tank RO without a permeate pump sends some water to drain for each gallon it makes, but I couldn't find Express Water's figure for the RO5DX.
- Membrane rejection rate beyond the general "reduces 99% of impurities" in the title.
- Warranty length on the listing I reviewed. Confirm it before buying.
None of these is a dealbreaker. They're the questions to ask if you're comparing it closely with the APEC.
What install day involves
Express Water says over half the system comes preassembled, but you're still making four connections under the sink:
- Feed water: a valve on the cold supply line. Tee it in after the softener if you want softened feed (better for the membrane).
- Drain: a saddle clamp on the sink drain, above the P-trap. Put it on the side away from the garbage disposal so food doesn't backflow into the line.
- Faucet: most sinks have a spare sprayer or soap-dispenser hole. On granite or quartz without one, you'll need to drill or hire someone who has the bit.
- Tank: set it upright somewhere you can reach the valve. Leave room for the five housings to come out at filter-change time.
After install, follow the manual's startup sequence: fill the tank, drain it fully, and repeat as instructed before drinking. The first tanks flush out carbon fines and anything left over from manufacturing in the new cartridges and membrane.
Quick answers
Will RO water corrode my pipes? The RO5DX only feeds its own faucet, so the rest of your plumbing never sees it.
Can I put it on hard water without a softener? Yes. It's rated for normal tap water within its pressure range. But scale builds up on the membrane faster with hard feed water, so membrane life may fall short of the one-year guideline. Track it with a TDS meter.
Does it need electricity? No. It runs on line pressure alone, which is why the 40 psi minimum matters.
Who should buy it
Yes: households of 1–5 on city water or softened water, with 40+ psi, who mostly want clean drinking and cooking water from a dedicated faucet.
No: low-pressure wells, homes feeding a fridge and ice maker plus heavy kitchen use, or anyone who doesn't like the taste of mineral-free water. RO water tastes very "clean," and some people find it flat.
Alternatives
APEC ROES-50. The same recipe (5 stages, 50 GPD, NSF/ANSI 58 and 372) from a different company. Pick between the two on warranty terms, filter availability where you live, and which faucet you prefer. Check price on Amazon
iSpring RCC7AK. A 75 GPD, 6-stage system with an alkaline remineralization stage. More output for bigger households or a fridge tie-in, and the mineral stage takes the edge off RO's flat taste. It has one more cartridge to replace. Check price on Amazon
Home Master TMAFC Artesian Full Contact. A 7-stage RO built around adding minerals back: Home Master's patented system adds calcium and magnesium twice during purification. It has larger fittings for a quoted 4.5-second fill of an 8 oz glass, a 50 gpd membrane and a 5-year limited parts warranty. It's for households whose main complaint about RO is the taste. It's a bigger install and a different cartridge format. Check price on Amazon
If 50 GPD and a plain five-stage setup fit your kitchen: Check price on Amazon