RKIN Flash Undersink Reverse Osmosis System
Tank-based undersink RO with a chrome lead-free faucet at $329.45, running on line pressure alone with no pump and no plug.
Undersink reverse osmosis usually starts around $500. The RKIN Flash lands a full RO system with a lead-free chrome faucet at $329.45, and it does it without a pump, a plug, or most of your cabinet.
Price: $329.45 · Verified: 2026-08-16
Undersink reverse osmosis usually starts around $500. The RKIN Flash lands a full RO system with a lead-free chrome faucet at $329.45, and it does it without a pump, a plug, or most of your cabinet.
The Flash is a tank-based undersink RO: a slim 5.5 by 14 by 16 inch filter housing plus a 3.2 gallon storage tank that sits vertically or horizontally, feeding a chrome gooseneck faucet at the sink. The 75 gallon per day membrane is, per RKIN, about 50 percent faster than most undersink membranes, and the whole system runs on household line pressure, no electricity and no pump noise. Cartridge changes use a twist-on mechanism the brand says eliminates leaky O-rings.
Two editions, same price. AlcaPure finishes with a remineralization post-filter that returns small amounts of calcium and magnesium, which RKIN states lands the water at 7 to 8 pH; we read that as a taste feature. OnliPure swaps that stage for deionization chasing a zero TDS reading. The RO stack upstream is identical, and RKIN includes a free TDS meter with the system so you can check the output yourself.
Where it gives ground: paperwork. RKIN states the RO membrane carries NSF/ANSI 58 certification and cites fluoride, chlorine, and heavy-metal reduction, but that is a membrane-level, brand-published claim rather than a whole-system listing we independently confirmed, and the Boroux Legacy's verified WQA listings set the certification bar in this category. This is also a real plumbing install, drain saddle included, so renters should look at RKIN's zero-install countertop units instead. And like all non-pumped RO, production slows on weak line pressure and reject water goes to the drain.
At $329.45 against a $499.95 compare-at, with a 1-year warranty, the Flash's pitch is simple: the cheapest credible way to put real reverse osmosis at your kitchen tap.
Homeowners who want plumbed-in reverse osmosis at the lowest credible price and are comfortable with a weekend DIY install under the sink.
You rent or cannot modify plumbing (RKIN's countertop units exist for exactly that), or you buy on independently confirmed certification listings, where Boroux leads this category.
Specifications
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RKIN Flash Undersink Reverse Osmosis System cross-shops across several editorial surfaces on this site: the full brand catalog and the in-depth guides for its category.
RKIN Flash Undersink Reverse Osmosis System - buyer FAQ
What is the difference between the AlcaPure and OnliPure editions?
Both editions cost the same $329.45. AlcaPure ends with a remineralization post-filter that returns small amounts of calcium and magnesium, which RKIN states lands drinking water at 7 to 8 pH. OnliPure swaps that stage for deionization aimed at a zero TDS reading. Pick by taste preference; the filtration upstream is identical.
Is the RKIN Flash NSF certified?
RKIN states the RO membrane carries NSF/ANSI 58 certification, a membrane-level claim we attribute to the brand rather than a system listing we independently confirmed. If a verified third-party listing is your deciding factor, the Boroux Legacy's WQA listings (NSF/ANSI 42, 372, and 401) are the strongest we confirmed in this category.
Does the Flash need electricity or a pump?
No. It is a non-electric, pump-less design that runs on household line pressure and fills a 3.2 gallon storage tank, which can sit vertically or horizontally under the sink. The filter housing itself is slim at 5.5 by 14 by 16 inches, leaving usable cabinet space. Weak line pressure slows production.
How hard is the install?
It is a standard undersink RO install: mount the housing, tee off the cold line with the included quarter-inch fittings, seat the 1.5 inch drain saddle, and mount the chrome lead-free faucet. RKIN includes the tank shut-off valve, tubing, and a refrigerator tee, and covers the system with a 1-year warranty.
Does the Flash waste water?
Yes, as all reverse osmosis does: reject water carries the concentrated dissolved solids to the drain. RKIN publishes a 75 gallon per day membrane rating but no waste ratio for the Flash, and non-pumped undersink systems typically send more to drain than pumped ones, so expect several gallons per purified gallon.