Do you ever take a sip of tap water and wonder exactly what you are drinking? Many of us worry about hidden contaminants like chlorine or heavy metals lurking in our everyday water. Choosing the best Reverse Osmosis (RO) under-sink system can feel like a huge task. You see so many brands and technical terms, and it’s easy to feel overwhelmed. Which one fits your kitchen? Which one actually cleans your water the best?
This confusion stops here. We understand the frustration of trying to balance budget, performance, and easy installation. In this guide, we break down everything you need to know about RO under-sink systems. You will learn the key differences between models, what features truly matter, and how to pick a system that gives your family pure, great-tasting water without the headache.
Ready to transform your kitchen tap water from questionable to crystal clear? Let’s dive into the details and find the perfect RO system for your home.
Top Ro Under Sink System Recommendations
- PATENTED DESIGN – The top-mounted fastener allows for easy countertop installation entirely from above, eliminating the hassle of tightening the nut from underneath the sink.
- MINERAL BOOST – The patent-pending natural mineral AK stage delivers spring water with a balanced, healthy pH and multiple essential minerals.
- SEE WHAT’S CAUGHT – The transparent first-stage filter housing makes it easy to monitor contaminant buildup, ensuring timely filter changes.
- NSF 58 CERTIFIED RO SYSTEM – Unlike other brands that lack NSF certification or full system certification, our RCC7AK is certified to NSF/ANSI 58 standards for the entire water filtration system.
- EFFECTIVE FILTRATION – Reduces TDS (93-98%), PFAS (96-99%), Chlorine (95-99%), Asbestos (>99.7%), Barium (>98.4%), Cadmium (>98.8%), Chromium (>99.2%), Copper (>97.8%), Fluoride (>97.4%), Lead (>98.9%), Selenium (>99.0%), and over 1,000 other contaminants.
- 𝐍𝐒𝐅/𝐀𝐍𝐒𝐈 𝟑𝟕𝟐 𝐂𝐞𝐫𝐭𝐢𝐟𝐢𝐞𝐝 & 𝟕-𝐬𝐭𝐚𝐠𝐞 𝐟𝐢𝐥𝐭𝐫𝐚𝐭𝐢𝐨𝐧 & 𝟒𝟎𝟎 𝐆𝐏𝐃 & 𝟏:𝟏 𝐥𝐨𝐰 𝐝𝐫𝐚𝐢𝐧 𝐫𝐚𝐭𝐢𝐨 & 𝐓𝐚𝐧𝐤𝐥𝐞𝐬𝐬 𝐃𝐞𝐬𝐢𝐠𝐧 & 𝐄𝐚𝐬𝐲 𝐢𝐧𝐬𝐭𝐚𝐥𝐥𝐚𝐭𝐢𝐨𝐧; Two filters are included in the package. Search "WD-G2-W" for replacement filters.
- 𝟕 𝐒𝐭𝐚𝐠𝐞 𝐅𝐢𝐥𝐭𝐫𝐚𝐭𝐢𝐨𝐧 & 𝐞𝐟𝐟𝐞𝐜𝐭𝐢𝐯𝐞 𝐟𝐢𝐥𝐭𝐫𝐚𝐭𝐢𝐨𝐧:The G2 system is certified by 𝐍𝐒𝐅/𝐀𝐍𝐒𝐈 𝟑𝟕𝟐 for lead-free materials. The G2 RO System adopts a composite filter result in more effective filtration. Our RO system can reduce TDS, PFAS, PFOA, PFOS, vinyl chloride, monobutyl ether, according to reverse osmosis membrane technical manual.
- 𝟒𝟎𝟎 𝐆𝐏𝐃＆𝟏:𝟏 𝐩𝐮𝐫𝐞 𝐭𝐨 𝐝𝐫𝐚𝐢𝐧 𝐫𝐚𝐭𝐢𝐨: The Waterdrop G2 reverse osmosis system offers a fast water flow rate of up to 400 GPD. Get a cup of filtered water in about 12 seconds, satisfying your needs while saving time. Compared to the ordinary RO system, the Waterdrop RO system always has a stable water flow. This tankless RO has a low drain ratio of 1:1 and saves water waste by 300%.
- 𝐈𝐧𝐧𝐨𝐯𝐚𝐭𝐢𝐯𝐞 𝐭𝐚𝐧𝐤𝐥𝐞𝐬𝐬 𝐝𝐞𝐬𝐢𝐠𝐧: The tankless design ensures the safety of your family’s drinking water. It also saves over 70% more under-sink storage space than does the ordinary RO system. Note that this reverse osmosis system requires under-sink electricity.
- 𝐈𝐧𝐭𝐞𝐠𝐫𝐚𝐭𝐞𝐝 𝐩𝐫𝐨𝐝𝐮𝐜𝐭 𝐝𝐞𝐬𝐢𝐠𝐧: The advanced integrated design of the electrical and water circuits reduces leakage. The airtight housing reduces noise, while the process of installing and replacing the filter is faster and more convenient than with other filters. Due to the filters’ twist-and-pull design, you can replace them in 3 seconds. The installation of the RO System takes less than 30 minutes. NOTE: An electrical outlet and drilling holes is required to operate it.
- Reverse Osmosis Water Filter: Experience what water should taste like with the Express Water reverse osmosis water filtration system reducing up to 99.99% of Lead, Chlorine, Fluoride, PFAs/PFOs, Calcium, Arsenic, and more.
- Water Purification System: Drink the healthiest water on Earth. All our water filters are specially engineered to work together, producing the safest and best tasting water you’ll ever drink
- Under Sink Water Filter: Don’t waste money on professional installation. Express Water’s quick and easy-to-understand design means you can install and understand everything about your new water filtration system
- Under Sink Water Filter System: No need to mess with refilling or activating your water filter, Express Water’s water filtration systems automatically fill your water tank with high quality drinking water
- Leak Detection: Each under sink water filter includes an emergency leak stop detector that shuts off water flow when it detects unwelcomed moisture
- 𝐓𝐫𝐮𝐬𝐭𝐞𝐝 𝐜𝐞𝐫𝐭𝐢𝐟𝐢𝐜𝐚𝐭𝐢𝐨𝐧𝐬: Waterdrop G3P600 reverse osmosis system is certified against NSF/ANSI 58 for TDS reduction and NSF/ANSI 372 certified for lead-free material. Also it has been tested and certified against NSF 42 to reduce chlorine, bad taste and odor. The tankless reverse osmosis system is also certified by the Federal Communications Commission. Besides, it meets the EU Standards and UKCA Standards for safety.
- 𝟖-𝐬𝐭𝐚𝐠𝐞 𝐟𝐢𝐥𝐭𝐫𝐚𝐭𝐢𝐨𝐧: Tested by official third-party laboratory (SGS), the reverse osmosis system can effectively reduce TDS, chromium, PFAS, radium, fluoride, arsenic salt, iron, calcium, particles, chloride, chlorine and radioactive substances in your tap water. And our RO water filter system can reduce chemicals such as vinyl chloride, ethylhexyl acrylate, isobutylene, ethylene glycol, according to the reverse osmosis membrane technical manual.
- 𝐒𝐦𝐚𝐫𝐭 𝐝𝐢𝐬𝐩𝐥𝐚𝐲 𝐟𝐚𝐮𝐜𝐞𝐭: The tankless reverse osmosis system is built with a smart display faucet. For instance, the TDS monitor tells you the quality of your filtered water, while the filter life tracker shows how soon you need to replace your filter.
- 𝐇𝐢𝐠𝐡 𝐜𝐚𝐩𝐚𝐜𝐢𝐭𝐲, 𝟐:𝟏 𝐥𝐨𝐰 𝐝𝐫𝐚𝐢𝐧 𝐫𝐚𝐭𝐢𝐨: As an upgraded reverse osmosis system, this reverse osmosis water system produces 600 gallons of filtered water per day. By its low drain ratio, this system can produce only one cup of waste water for every two cups of pure water produced. Furthermore, with a fast and stable water flow rate, this RO system fills a 8 oz cup of water in 8 seconds, which is ideal for drinking and washing vegetables.
- 𝐓𝐚𝐧𝐤𝐥𝐞𝐬𝐬 𝐝𝐞𝐬𝐢𝐠𝐧: Waterdrop G3P600 reverse osmosis system has a stylish look. This tankless design saves 70% under sink space. You can change a filter in 3 seconds without moving the system or using any tools. Note: This reverse osmosis system requires under-sink electricity.
- [Note] Two holes must be drilled for installation. One on the countertop for the RO faucet and a second under the sink for the drain pipe. An electrical outlet is also needed.
- [NSF/ANSI 372&53&42 Certified & 9-Stage Filtration System & 600GPD & 3:1 Low Drain Ratio & Tankless & Easy Installation.] Two filters (1 RO+1 PCB) are pre-installed in the unit.
- [9 Stage Filtration System & Tested by SGS] Viomi reverse osmosis water filter features a 0.0001μm membrane for superior purity. SGS Certified to NSF/ANSI standards 372, 53, and 42, it's proven to reduce PFAS contaminants like lead, fluoride, and PFOA. Enjoy exceptional purity with a TDS reduction of up to 94.75% and PFOS/PFOA reduction of up to 99.60%.
- [600 GPD, 3:1 Pure to Drain] The Viomi VORTEX 6 reverse osmosis system delivers over 1 ounce of water per second, saves your precious time while satisfying your need. The tankless design and a low 3:1 pure-to-drain ratio help you save up to 300% more water compared to traditional systems.
- [Compact Tankless Design] Say goodbye to bulky tanks. Viomi tankless ro system measures just 16.3"D x 5"W x 12.8"H, saving up to 65% of under-sink space. It's designed to fit easily in most kitchen cabinets.
- 𝐀𝐝𝐯𝐚𝐧𝐜𝐞𝐝 𝟗-𝐒𝐭𝐚𝐠𝐞 𝐅𝐢𝐥𝐭𝐫𝐚𝐭𝐢𝐨𝐧：The Waterdrop Reverse Osmosis Water Filter — WD-T3-M uses advanced 9-stage filtration to reduce heavy metals, chlorine, PFOA & PFOS with a 0.0001μm RO membrane, while enriching water with minerals for better taste and health. *Tested by a third - party laboratory.
- 𝐋𝐄𝐃 𝐋𝐢𝐠𝐡𝐭 & 𝐀𝐮𝐭𝐨-𝐅𝐥𝐮𝐬𝐡：Just install and 𝐩𝐥𝐮𝐠 𝐢𝐧 this under-sink RO water filtration system for instant pure refreshment. With an LED light and continuous automatic flushing, every cup of water you get is crisp, clean, and at its purest and freshest. 𝐍𝐨𝐭𝐞: This system requires an electrical connection for operation.
- 𝐌𝐢𝐧𝐞𝐫𝐚𝐥-𝐈𝐧𝐟𝐮𝐬𝐞𝐝：Enjoy mineral-rich water with our advanced reverse osmosis system. Infused with calcium, magnesium and other essential minerals, it enhances the taste of drinks while supporting bone health and daily hydration needs.
- 𝟒𝟓𝟎𝐆𝐏𝐃 𝐅𝐚𝐬𝐭 𝐅𝐥𝐨𝐰 & 𝐒𝐦𝐚𝐫𝐭 𝐀𝐥𝐞𝐫𝐭𝐬：Experience fast, steady 450GPD water flow. Our under-sink RO system's smart alerts remind you when to replace filters, and the all-in-one cartridge enables effortless replacement in seconds — making pure water drinking completely effortless. 𝐏𝐥𝐞𝐚𝐬𝐞 𝐧𝐨𝐭𝐞: Faucet installation requires drilling holes in the countertop.
- 𝟐:𝟏 𝐏𝐮𝐫𝐞 𝐭𝐨 𝐃𝐫𝐚𝐢𝐧 & 𝐋𝐨𝐧𝐠-𝐋𝐚𝐬𝐭𝐢𝐧𝐠 𝐅𝐢𝐥𝐭𝐫𝐚𝐭𝐢𝐨𝐧：Experience eco-efficiency with our ultra-saving tankless reverse osmosis system, boasting an unparalleled 2:1 pure-to-drain ratio, saving precious water resources. The 6-month CF filter, 12-month CBM filter, and 24-month RO filter lessen replacement hassles and help the planet, ensuring a sustained clean water supply.
- 8-STAGE FILTRATION - Stokk 8-stage 0.0001μm RO filtration system effectively removes 1000+ contaminants by 99.99%, including TDS, PFAS, PFOA, PFOS, fluorides, chlorides and more
- TESTED AND CERTIFIED BY SGS - Against from NSF/ANSI 58& 42American National Standard & EPA 200 standard, tested and certified by SGS to effectively eliminate the hidden risks of tap water. Also FCC Certified. Scan the QR for SGS online test report
- Tankless Design: Unlike traditional RO water filtration systems, the Stokk tankless reverse osmosis system boasts a sleek, space-saving design. It saves over 75% of under-sink space and prevents recontamination, making it perfect for American kitchens. Installing the Stokk RO system is a breeze and can be done in just 30 minutes. Save time and upgrade your kitchen now
- TASTE IMPROVING - Reverse osmosis system adapts a composite filter technology, combining pre-activated carbon filter and post carbon filter to effectively reduce odor and chloride. The unique Coconut-shell activated carbon post filter further absorbs odors and residual chlorine, makes it more purer, fresher
- High Capacity & 2:1 Pure to Drain Ratio: Offer a higher water capacity, which meets demands of family for top-quality water. This tankless RO system saves water waste by 800% compared to traditional under sink RO system. Stokk's home RO water filter system is the optimal choice for those seeking high-performance water filtration
- ALKALINE FILTRATION WITH SLEEK BLACK FAUCET - This advanced 6-stage RO system restores natural alkalinity and essential minerals, delivering better-tasting water compared to standard 5-stage systems. The included black RO faucet enhances your kitchen’s style with a modern, sophisticated touch.
- EFFICIENT IMPURITY REDUCTION - Reduces up to 99% of over 1,000 harmful contaminants, including sediment, vinyl chloride, chlorine, fluoride, lead (98%), arsenic, PFAS, asbestos, calcium, and sodium, ensuring clean, pure drinking water.
- LOW MAINTENANCE - Features a transparent first-stage filter housing for quick visual inspection. Three pre-filters protect the RO membrane, which filters contaminants down to 0.0001 microns, while a fine GAC filter provides a finishing touch. The AK filter restores minerals and alkalinity for fresh, great-tasting water.
- DIY INSTALLATION WITH LEAK PROTECTION - Designed for hassle-free installation with all necessary parts included. Backed by a clear manual, instructional videos, and lifetime technical support. Quick-fitting connectors ensure a leak-free setup without the need for threading pipes. Note: Please check under-sink space before purchasing.
- 100% SATISFACTION GUARANTEED - Register for a 1-year limited manufacturer warranty and enjoy dedicated support from our team in GA, USA. Built with premium components for a long-lasting supply of bottled-quality drinking water, promoting a plastic-free future.
The Ultimate Buying Guide: Choosing Your Perfect RO Under Sink System
An RO (Reverse Osmosis) under sink system is a fantastic way to get clean, great-tasting water right from your kitchen tap. These systems filter out many impurities. Buying the right one means looking closely at what matters most. This guide helps you pick the best fit for your home.
Key Features to Look For
When shopping, certain features make a system better or easier to use. Pay attention to these:
Filtration Stages
- Number of Stages: Most good systems have 4 to 7 stages. More stages usually mean better filtration. The basic stages include sediment filters, carbon blocks, and the RO membrane itself.
- Post-Carbon Filter: This stage polishes the water, making it taste great right before it reaches your faucet.
Tank Size and Flow Rate
- Storage Tank: RO systems create purified water slowly. The tank stores this water. A standard family needs a 3-gallon or 4-gallon tank. If your family is large, look for a bigger tank.
- Gallons Per Day (GPD): This tells you how fast the system makes new water. Higher GPD means faster refills.
Maintenance and Monitoring
- Filter Life Indicators: Some advanced models tell you when to change the filters. This takes the guesswork out of maintenance.
- Easy-Change Filters: Some filters twist on and off easily. Others require more tools and time to replace.
Important Materials Matter
The materials used in your RO system affect its safety and how long it lasts.
Housing and Tubing
- BPA-Free Plastic: Ensure all plastic parts that touch the drinking water are certified BPA-free. This keeps harmful chemicals out of your water.
- Food-Grade Tubing: The tubing should be high-quality, usually polyethylene, ensuring water purity from the system to your faucet.
Membrane Quality
The RO membrane is the heart of the system. Look for membranes made by trusted brands. A good membrane lasts longer and filters more effectively.
Factors That Improve or Reduce Quality
What makes one system superior to another? It often comes down to efficiency and build quality.
Improving Quality
- High Rejection Rate: A good RO membrane rejects 95% or more of the total dissolved solids (TDS) in the incoming water.
- Leak Protection: Systems with automatic shut-off valves or leak-detection mats are safer. They prevent major water damage if a connection fails.
- Low Drain Ratio: Older systems waste a lot of water down the drain for every gallon purified. Newer, high-efficiency models reduce this waste significantly.
Reducing Quality
- Cheap Plastic Components: Units using very thin or uncertified plastic might break down faster or leach chemicals.
- No Pre-Filters: Systems skipping the initial sediment or carbon pre-filters will quickly clog and ruin the expensive RO membrane.
User Experience and Use Cases
Think about how you will actually use the system day-to-day.
Installation
Most under sink systems require drilling a small hole in your countertop for the dedicated faucet. If you are not handy, check if professional installation is easy to arrange. Some systems offer quick-connect fittings, which make DIY installation much simpler.
Noise Level
RO systems are usually quiet. However, if the system includes a booster pump (often needed for low-pressure homes), it might make a slight humming noise when actively making water. This is something to consider if you have an open-concept kitchen.
Best Use Cases
- Drinking Water: The primary use is for pure, great-tasting water for drinking and making coffee or tea.
- Cooking: Using purified water for cooking vegetables or making ice cubes can improve the taste of your food.
10 Frequently Asked Questions (FAQ) About RO Under Sink Systems
Q: What exactly does an RO system remove from my water?
A: RO systems remove most contaminants, including heavy metals like lead, chlorine, fluoride, bacteria, pesticides, and high levels of total dissolved solids (TDS).
Q: How often do I need to change the filters?
A: Pre-filters and post-filters usually need changing every 6 to 12 months. The main RO membrane lasts much longer, typically 2 to 5 years, depending on your incoming water quality.
Q: Will an RO system make my water taste flat?
A: While RO removes everything, including healthy minerals, the final “polishing” carbon filter usually adds a pleasant taste back. If the water tastes too flat, you might look for a system with a remineralization stage.
Q: Does the system need electricity to run?
A: Standard, non-pumped systems do not need electricity. However, systems with booster pumps to increase water pressure require a standard electrical outlet nearby.
Q: How much space do I need under my sink?
A: You need enough space for the storage tank, which is usually about the size of a small office trash can, plus room for the filter manifold.
Q: Is RO water safe for babies or pets?
A: Yes, RO water is very safe. Some pediatricians suggest adding a small amount of bottled mineral water back into formula if you are concerned about the complete lack of minerals, though this is not usually necessary.
Q: What happens if my water pressure is very low?
A: If your home pressure is low, the system will produce water very slowly or not at all. You should choose a model that includes a built-in booster pump for optimal performance.
Q: Does installing an RO system affect my regular hot and cold water lines?
A: No. The RO system taps only into the cold water line. It adds a separate, small faucet just for the purified water.
Q: What is TDS, and why is it important?
A: TDS stands for Total Dissolved Solids. It measures everything dissolved in the water—minerals, salts, and metals. Lowering the TDS is the main goal of an RO system.
Q: Can I connect the RO system to my refrigerator’s ice maker?
A: Yes, most RO systems come with an extra connection valve that allows you to divert the purified water line to supply your refrigerator’s ice maker and water dispenser.