Reverse Osmosis Water Filters for Under-Sink Install. From standard RO to the full hydration stack.

A reverse osmosis water filter is an under-sink water filtration system that uses household water pressure to force tap water through a semipermeable membrane with a pore size of approximately 0.0001 micron. The membrane blocks dissolved contaminants (lead, PFAS, fluoride, arsenic, pharmaceuticals, and total dissolved solids) and allows filtered water to pass through into a storage tank below the sink. The filtered water is delivered through a dedicated faucet at the countertop. Reverse osmosis is the most comprehensive consumer-grade contaminant reduction method available, and is one of the few methods certified by NSF/ANSI for PFAS reduction at the household level.

The best reverse osmosis system depends on your water and your priorities. For the tightest budget, and for buyers who want mineralization built into the unit, the GoodFor Pur-Alk Standard is a 6-stage RO with a built-in alkaline mineral filter. For standard municipal water and NSF-certified entry RO, the MicroMax 7000 is a 4-stage system covering chlorine, lead, and standard contaminant reduction. For homes concerned about PFAS, fluoride, pharmaceuticals, or emerging contaminants, the MicroMax 8500 adds NSF/ANSI 53 certification for 99% PFOA/PFOS reduction and NSF/ANSI 401 for pharmaceutical reduction. For households that want the complete drinking water setup (filtration plus mineral restoration plus structuring), the Hydration Stack combines the MicroMax 8500 with the Sango Coral remineralization filter and the UMH Pure structuring device.

The GoodFor Pur-Alk Standard is a 6-stage under-sink reverse osmosis system with built-in alkaline mineralization. The six stages are: a sediment pre-filter (Stage 1), two dual-pass carbon dechlorination stages (Stages 2 and 3), an RO membrane (Stage 4), a post-carbon block polish from the storage tank (Stage 5), and an alkaline mineral filter as the final stage (Stage 6). It reduces chlorine, dissolved metals (lead, copper, cadmium, chromium), dissolved solids (sodium, selenium, arsenic, nitrates, nitrites), waterborne cysts, and dissolved pharmaceuticals. The Pur-Alk Standard is the budget-friendly entry into under-sink RO and the only GoodFor RO with mineralization built into the unit rather than a separate cartridge. It operates without electricity on household water pressure, fits under any standard kitchen sink, and is apartment-compatible when paired with the optional dual-function kitchen faucet.

The MicroMax 7000 is a 4-stage RO with three physical cartridges (a combined sediment/UF cartridge, an RO membrane, and a post-carbon polish). It is certified to NSF/ANSI 42, 53, 58, and 372, covering chlorine, lead, VOCs, and standard RO performance.

The MicroMax 8500 is a 5-stage RO with four physical cartridges plus an integrated UF stage built into the manifold. It adds a dedicated PFAS-grade GAC carbon stage and carries additional certifications: NSF/ANSI 401 for emerging contaminants (BPA, estrone, ibuprofen, naproxen) and CSA B483.1. The MM8500 is the only GoodFor RO certified for PFAS (PFOA/PFOS at 99% reduction) and pharmaceutical reduction. It is also the RO component inside the Hydration Stack.

Reverse osmosis works by pushing water against a semipermeable membrane under pressure. Normal osmosis moves water across a membrane from low-solute concentration to high-solute concentration; reverse osmosis runs the process backward, forcing water from the contaminated (high-solute) side to the filtered (low-solute) side. Household RO systems use the natural pressure in your cold water line, typically 40 to 100 psi, to push water through the membrane. Dissolved contaminants are physically blocked by the membrane and flushed to drain. Filtered water collects in a sealed storage tank and is delivered through a dedicated faucet on demand. No electricity is required.

A properly certified reverse osmosis system reduces the following contaminants. Reductions cited here are for the GoodFor MicroMax 8500, tested and certified to NSF/ANSI 58:

Heavy metals and dissolved solids: Lead (96.3%), arsenic pentavalent (97.3%), arsenic trivalent (98.9%), copper (98.8%), selenium (over 99.1%), radium 226/228 (80%), TDS (93.8%).

Disinfection byproducts and additives: Chlorine (NSF/ANSI 42), fluoride (96.5%).

Emerging contaminants: PFOA/PFOS (99%), BPA (95%), estrone (96%), ibuprofen (~95%), naproxen (96%), nonylphenol (92%), all certified to NSF/ANSI 401.

Microbiological and particulate: Cryptosporidium and Giardia cysts (via the ultra-filtration stage), turbidity (over 99.1% at 11 NTU influent).

Yes. Properly certified RO systems reduce all three. The GoodFor MicroMax 8500 is certified to NSF/ANSI 53 for 99% PFOA/PFOS reduction, NSF/ANSI 58 for 96.3% lead reduction, and NSF/ANSI 58 for 96.5% fluoride reduction. The MicroMax 7000 is NSF/ANSI 53 certified for lead reduction but is not specifically certified for PFAS or fluoride. Both the MicroMax 8500 and the Hydration Stack address the full panel of NSF/ANSI 53, 58, and 401 contaminants. The U.S. EPA established Maximum Contaminant Levels for PFOA and PFOS in 2024.

Drinking RO water in normal quantities is not harmful for healthy adults. RO strips nearly all dissolved minerals along with contaminants, however, leaving water slightly acidic (pH 6.0 to 7.0) and mineral-empty. The World Health Organization's 2009 report on calcium and magnesium in drinking water formally noted the public health significance of these minerals for cardiovascular and metabolic function. According to the NIH Office of Dietary Supplements, most adults in the U.S. do not meet recommended magnesium intake from diet alone, so water that contributes to mineral intake rather than being mineral-empty has practical value. For households where RO is the primary source of drinking and cooking water, many practitioners support adding mineralization. GoodFor offers two paths: the Pur-Alk Standard includes an alkaline mineral filter built directly into the unit as Stage 6, or the Sango Coral cartridge can be added inline to any RO system. It adds 70+ trace minerals at the natural 2:1 calcium-to-magnesium ratio and is the second stage of the Hydration Stack.

Reverse osmosis flushes a portion of incoming water to drain to carry away the rejected contaminants. There is no way around this; the contaminants have to go somewhere. The GoodFor MicroMax 7000 operates at a recovery rate of approximately 30.6%, meaning roughly 3 gallons of input water produces 1 gallon of filtered water, with the remainder flowing to drain. Higher input pressure improves the recovery rate. In practical terms, for a typical household consuming 3 to 5 gallons of drinking and cooking water per day, drain water from RO is a small fraction of overall household water use: typically a few percent of total daily consumption, often less than what a single load of dishes uses. The water savings versus bottled water (in production, packaging, and transport) are substantially greater than the drain water cost.

A licensed plumber is strongly recommended, though not strictly required. Installation involves tapping into the cold water supply line, connecting to the drain, and drilling a hole in the countertop or sink deck for the dedicated faucet. The optional dual-function kitchen faucet, sold separately, installs through your existing faucet hole instead, with no drilling. A typical professional install takes 60 to 90 minutes. In GoodFor's full-service markets (Southern California, Houston, Austin, Tampa, and Miami/Fort Lauderdale), installation is handled directly by our licensed master plumber team led by co-founder Boris Jabotinsky (CSLB #1102129). Outside those markets, every order ships nationwide with 24/7 Installation & Service Concierge: your local plumber gets a free video call with ours and standing access for the life of the system.

Replacement intervals depend on the system and household usage. The MicroMax 7000 has staggered intervals: the carbon block / UF cartridge replaces every 6 to 12 months depending on chlorine load, the RO membrane lasts 2 to 3 years, and the post-filter replaces every 12 months. The MicroMax 8500 uses a simplified maintenance schedule: all four cartridges replace together on the same 12-to-18-month interval, so a single service visit handles the entire system. Both systems have a design capacity of approximately 2,500 gallons per cycle; gallons through the system, not the calendar, ultimately drives the cycle. Subscribe & Save is available on all replacement cartridges.

Under-sink RO systems install under the kitchen sink, connect to the cold water supply line, and deliver filtered water through a dedicated faucet. The storage tank lives under the cabinet. Countertop RO systems sit on the kitchen counter, fill manually or via a hose connection, and dispense from a built-in spigot or tank. Under-sink systems are higher capacity, hidden, and dispense water on demand without manual refilling, but require professional installation. Countertop systems are portable, easier to install (some are renter-friendly with no plumbing changes), and lower capacity. For full-time household drinking water use, especially for families, an under-sink system like the GoodFor MicroMax 7000 or MicroMax 8500 is the more practical choice.

The standard Hydration Stack ships with the MicroMax 8500 as the RO component, the version certified for PFAS, pharmaceuticals, and emerging contaminants. A budget-friendly version can be configured with the MicroMax 7000 in place of the 8500, paired with the same Sango Coral cartridge and UMH Pure. This configuration delivers filtration, remineralization, and structuring, but without the NSF/ANSI 53 PFAS certification or NSF/ANSI 401 pharmaceutical certification of the standard Stack. If you would like to configure a custom Stack, book a free consultation and our team will scope it against your water data.

Yes. The GoodFor Sango Coral cartridge is designed to work with any reverse osmosis system, not only GoodFor's MicroMax 7000 or 8500. It is available in both ¼" and ⅜" John Guest quick-connect push-fit sizes, the two universal under-sink RO line standards, so it pairs with virtually any existing setup. Pairing it with the UMH Pure structuring device gets you Hydration-Stack-level drinking water without replacing the RO system you already own. This is the upgrade path most customers with an existing RO choose.