Waterdrop Reverse Osmosis

This means you can install it in any kind of sink or faucet. This intelligent design also allows you to change the filters with the utmost convenience.
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smosis Water Filtration

NSF Certified performance

High Flow Compac

2-in-1 composite filter

GreatWell ROG400

3-stage filtration process

iSpring RCS5T, 500

5-stage filtration

SimPure Q6

Saves up to 70% of space

Best Tankless Reverse Osmosis Systems in 2021

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The search is over. Today marks the day that we deliver to you one of the essentials that have been missing from your home—the best tankless reverse osmosis system.


We understand that you want to get your money’s worth every time you buy a product. We also know how stressful it is to visit your local hardware or home appliance store and ask about the product you’re looking for. Don’t worry; we took the trouble upon ourselves and came up with this in-depth review.

In this heated battle, only one should come out on top. We’ll discuss in great detail all the other options to guarantee that you’d be able to make the right choice. We won’t keep this any longer.

Waterdrop Reverse Osmosis Water Filtration System, WD-G3-W

Top Features

  • NSF Certified performance
  • Seven stages of filtration
  • Internal pump
  • Low drain ratio
  • Chemical-free
  • Intelligent design

Why is the Waterdrop WD-G3-W tankless RO System on this list? Well, what we can say is that the conceptualization that has gone through the manufacturing of this product is very detailed and well thought of.

You will see lots of filtration systems out there that are NSF-certified, but with this unit, you can safely assume that it’s perfectly safe because it’s NSF 58 and NSF 372 certified. This means that contaminants like limescale, fluoride, lead, and other heavy metals, are safely filtered by the Waterdrop reverse osmosis device.

The wonders of a seven-stage filtration system…

This cleansing of water is done through seven stages of the filtration process. The water goes through carbon and pre-sediment filters before finally reaching the RO membrane filter.

Carbon granules are used on the filters, with the addition of coconut shells, giving the water a distinct taste while purifying it, as well.


  • Slightly more expensive than your usual unit


  • Limited 5-year frame and 2-year parts warranty

Alkaline Remineralization High Flow Compact RO System, Frizzlife PD600

Top Features

  • Under-sink installation
  • 2-in-1 composite filter
  • Alkalization and remineralization method
  • Water-saving technology
  • LED display

The most notable feature of this product from Frizzlife is its under-sink filtration system. It took the definition of space-saving to a whole new different level.

To maximize the fact that this unit is tankless, more countertop space is saved when you have a compact PD600 Filter that you can install under the sink.

Four-stage filtration

The reverse osmosis process is done with a two-in-one composite filter that cleanses the water through four stages.

With a 0.0001 micron filter, you can guarantee that more than a thousand harmful chemicals will never get to flow out of your faucet. These include fluoride, chlorine, lead, and other chemicals or heavy metals.


  • Saves much-needed countertop space
  • Alkaline and pH balancing technology
  • Saves up to 450% water
  • High-tech design
  • Displays essential information about the filters


  • LED display requires an electricity source

GreatWell ROG400 with 400GPD RO Filter

Top Features

  • Low drain ratio
  • 3-stage filtration process
  • Leak-proof water route
  • Efficient design
  • NSF certified

If you’re looking for something that’s simple yet efficient, compact yet straight to the point, you should check out the GreatWell tankless reverse osmosis. You wouldn’t break a sweat installing this system, and changing the filters is relatively easy, as well.

This is equipped with an indicator that lets you know when you need to replace them. The compact design also enables you to save up to 30% space that can be used for other kitchen essentials.


  • Lessens water consumption
  • Purified, chemical-free water
  • FDA approved materials
  • Space-saving
  • Individual filter change indicators
  • Fast water flow


  • Water only goes through 3 stages of filtration

iSpring RCS5T, 500 GPD Commercial Grade

  • Top Features

    • 5-stage filtration
    • Dual-flow membrane
    • Low drain ratio
    • Booster pump
    • Drinking faucet
    • Tech support in installation

If you want the short answer, it’s a resounding, yes! The RCS5T iSpring boasts a dual-flow membrane without having to sacrifice its drain ratio. What that means is that this unit receives water from two sides and filters it simultaneously.

Skeptics would think that this dual-membrane mechanism will overwhelm the filtration process, but don’t worry. This unit is equipped with five-stage filtration to keep up with the water flow.

The first stage removes larger particles, while the second stage absorbs any byproduct of disinfection like chlorine and smell. The third stage acts as a safety net for any residue left by the second stage, which also helps prolong the lifespan of the membranes.

The fourth stage gets rid of viruses and bacteria, and finally, the last stage acts like a gate that removes any other residue to provide you with a cleansed and drinkable water.


  • Dual-flow membrane allows you to filter more water
  • Low drain ratio lessens water consumption
  • 5-stage filtration guarantees purified water
  • Fast water flow
  • Drinking faucet is equipped with water pressure gauge


  • No indicator for filter life

SimPure Q6

Top Features

  • NSF certified
  • 4-stage filtration
  • Sleek design
  • Low drain ratio
  • Filter change indicator

Here’s what we do know, SimPure RO has got all the basics covered.

First and foremost, since safety should always be our top priority, it’s important that we mention the fact that water purified by SimPure is NSF certified. This means that you won’t find any contaminant that may compromise the safety of your water as it undergoes a 4-stage filtration process.

The slim design of Q6 also lets you save up to 70% countertop space that may otherwise be used for other household essentials.

To maximize the idea of saving, this device also has a low drain ration at 1.5 to 1, reducing your total water consumption. Despite the low drain ratio, SimPure delivers water at a rate of 400 GDP.


  • Safe from contaminants
  • Saves up to 70% of space
  • Reduces water consumption
  • Fast water flow rate
  • Comes with a faucet
  • Filter life indicator


  • The faucet needs its own installation

Why Choose a Tankless RO System

All of this discussion about the tankless reverse osmosis system brings out one important question that must be answered: Why bother?

Why do you really need this equipment in your kitchen? Sure, you want the convenience of drinking water right from the faucet safely, but is there more to it?

Well, let our list of benefits answer for you.

1. It saves space.

One of the most important benefits of tankless RO filtration systems is the amount of space you’ll be saving. You certainly need lots of space in your kitchen top, and you don’t want an entire tank of water reservoir just sitting there.

With the slim designs and under-sink options of tankless water filtration systems, you don’t have to worry about that.

2. It offers instant and unlimited supply.

Another essential benefit of a tankless RO filtration system is the fact that you don’t need to get your drinking water elsewhere.

Since this filtration system basically transforms tap water, making it purified and drinkable, you can have clean water at your disposal.

What’s more, the supply will never run out!

3. It offers less risk of contaminants.

One downside of filtration systems with a tank is that there is the fact that water is still stored in a container. This heightens the risk of your water being unsafe.

One small mishap and your water reservoir can easily get contaminated, leading to gallons of waste water. Since tankless RO filtration systems do not need a container, the risk of contaminants is significantly reduced.

How Does a Tankless Reverse Osmosis System Work?

Basically, a tankless RO system works by using membranes to filter water. More often than not, these systems are equipped with three membranes. The main difference is how these membranes function.

In some tankless reverse osmosis systems, membranes can only provide three stages of water purification. However, some manufacturers have taken it up a notch and found a way to develop RO systems that can filter water for up to five or even seven times.

Through this process of filtration, ions, as well as any large or unwanted particles that may otherwise be harmful if ingested, are removed from the water composition. Reverse osmosis utilizes pressure to get rid of these particles and eventually provide you with purified water.

Important Features to Consider Before Buying

Because of the wide variety of options, it may be difficult to find the single, most suitable tankless RO filtration system for everyone. It will ultimately depend on what you want and need.

However, you still need to take note of these few reminders before getting yourself a filtration system.


Water filtration systems vary greatly in sizes. Some are slim, while others are quite big.

If one of the reasons why you opt for a tankless filtration system instead of those systems with a tank is to save space, make sure that you choose one that fits in your kitchen, or can be placed under the sink.

Filtration Stages

Even though all of these products claim to undergo reverse osmosis procedures, the quality of the water that is filtered may be very different. That’s because of the filtration stages that the water undergoes.

Make sure that you go for those filtration systems that have various purification stages to ensure that your water is cleansed and safe to drink.

Additional Features

Perhaps one of the main reasons why we want a tankless RO system is that it’s convenient. Since you’re already on that path, why not maximize it and go for those systems that are equipped with additional features like water pressure gauge or filter life indicator?


Is distilled water the same as reverse osmosis water?

Distillers attempt to purify water by removing unwanted minerals. One quick example is sodium. However, distillers are not capable of removing other harmful chemicals.

Lots of cities around the globe use chlorine or chloramine to purify the water. If you want to drink water directly from your faucet, don’t expect distillers to cleanse it. Removing chemicals like these is a job for reverse osmosis systems.

Does reverse osmosis waste water?

No water is totally wasted by RO systems. Only the amount of water produced changes. Reverse osmosis systems cleanse the tap water in the same way that we clean our dishes and clothes. It needs water to get rid of the impurities.

The amount of water purified, and the amount of water used to purify is indicated by the drain ratio of the different RO filtration systems.

How long will my reverse osmosis system last?

Proper maintenance of reverse osmosis systems allows you to use them for decades, provided that you replace filters when needed.

Usually, membranes can last up to five years. However, when the water it regularly purifies is riddled with chemicals, it may only last for three years or shorter.


This concludes the battle of the six best tankless reverse osmosis systems that you may find. After careful consideration of all the different features of these systems, we have concluded that the system that will give you the purest water is the Waterdrop WD-G3-W.

The fact that water filtration undergoes seven stages guarantees that the quality of water produced by this system is of topmost quality.

However, always keep in mind that what matters most is what your home needs. Once you’ve determined what that is, it will be effortless to find the water filtration system for you.