advantage and disadvantages of water filter
Since 2015, some companies have regarded "large flux tankless water filter" as a new selling point.

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Since 2015, some companies have regarded “large flux tankless water filter” as a new selling point. Some even abandon the traditional 50-gallon low-capacity tank water filter. And develop large-capacity tank-less products. To increase the production capacity up to 400-800 gallons. What is the difference between high-capacity products and low-capacity products? Will it be the development trend of the household water purifier market? Will it safer? Will it stable and good user experience?

advantage and disadvantages of water filter


What does 50G mean for household water filters?

First learn a G (gallon) unit conversion, 1 gallon (US) is approximately equal to 3.8 litres. By calculation, you can know the capacity of a 50-gallon is about 8 litres per hour, 133 ml per minute.

The national standard GB/T 22090-2008 stipulates the flow rate should not be less than 0.8 litres per minute. The water flow rate is too low to wait a long time.


Why is the capacity of traditional household water filter mostly 50 gallons?

Now, let’s analyze if a standard family of 5 people needs 4 litres of purified water per person per day. Including drinking, cooking, soup, etc., this value has considerable redundancy. The purified water required per day is 20 litres.

Then, the 20 litres of water demand time are concentrated into the morning, noon and evening. Each period is about 1 hour. Then the water capacity will be 7 litres per hour.

As far as the filter has a capacity of 8 litres per hour, there is no problem meeting the everyday needs. This is why the water capacity of the household filter is mostly 50 gallons.


What are the problems with a traditional water filter?

Why is a 50-gallon water purifier equipped with a storage tank?

The 50-gallon water purifier has a new problem in actual use. The production capacity of 1 minute is only 133 m. It means that it takes about 2 minutes to receive a glass of water (about 250 ml). This is unbearable by consumers.

For this problem, a 3 gallon (about 11 litres) pressure tank is necessary. The water is first stored in the water storage bag in the pressure tank. When needed, the water storage bag’s water is squeezed out by the pressure in the tank. And the water output can reach about 2 litres per minute. It is far higher than the national standard of 0.8 litres per minute.

In this way, the waiting time for taking a glass of water is about 8 seconds. With such a flow rate, the consumer experience during use should be very comfortable. So the 50-gallon household water filter will work with a 3-gallon storage tank. It is our typical household small flux tank water filter.

In reality, most household water use is concentrated in the morning, noon, and evening. There are 4 hours between each peak period. In these few hours, the water storage tank is full. Within each period, the water flow can ensure consumers’ regular and comfortable use.

As mentioned earlier, traditional household water filter work with pressure water storage tanks. And the storage bag inside is made of food-grade rubber material. It will have some rubbery smell, and absorbed by water and affects the taste of the water.

A post activated carbon is necessary to improve the taste. So, after RO treatment, water will pass through storage tank, post-carbon and then flow out.

Usually, a qualified household water filter must meet three basic requirements:


Being able to drink directly is a vital sign of a pure water machine.

There are high requirements on the capabilities and the wading material. When the membrane’s quality is defective or unqualified, the effluent will be contaminated. It’s not drinkable, not even for drinking directly.


The replacement cost of the filter element and related accessories should be reasonable.

As a household water filter, the membrane’s replacement is the primary consumption in the later use process. The processing capacity of the reverse osmosis membrane varies significantly in its price. It determines the cost of other corresponding pretreatment filter elements and booster systems. Good configuration.

Thus, choosing the right capacity RO membrane has become the key to high cost-performance.


Avoid unnecessary waiting; the flow rate should be enough.

In actual use, if the flow of purified water is less than 1 litre per minute, the consumer experience will not be good.

Usually, the traditional small capacity filter can meet the above three requirements.

But, the material and manufacturing of storage bag and carbon are not very good. It directly causes the total number of bacteria and nitrite in the water to exceed the standard. Some also have serious problems such as excessive heavy metals. These have once appeared in the market—a worrying situation.

In response to this situation, two solutions have emerged.

The first is to follow the technical requirements strictly. Ensure the use of food-grade materials. Cut the root cause of secondary pollution.

The second is to use a large-capacity reverse osmosis membrane. And enough capacity to cut the storage tank and the post-activated carbon configuration.

Based on the second solution, when removing the tank, the user will save a lot of installation space. In this case, an enormous capacity tankless pure water filter appears.

Let's summarize:

First, for the family’s daily consumption, the 50 gallons of capacity is very much surplus. It also considers the three factors. Including:

  • Temperature drop, 
  • An increase of pollutant content, 
  • The middle and late stages of reverse osmosis membranes. 

In actual use, these three factors will reduce membrane production capacity.

Second, with a tank, we can always guarantee water flow and reduce production capacity. And provide more than 2 litres per minute. The decrease in production capacity has nothing to do with the flow of purified water. The whole process has a stable water output and a good consumer experience. That’s why this kind of filter can become a traditional product on the market today.


Advantages and disadvantages of large capacity tankless water filter

Let me talk about a feature of a reverse osmosis membrane:

After stops running, still some pure water and wastewater in the membrane shell. No external pressure, there is osmotic pressure between the wastewater and purified water. There will be a two-way penetration process.

With the extension of permeation time, the pure water concentration will gradually increase.

The longer the downtime, the higher the TDS of the pure water in the membrane. When the output TDS reaches 50% of input, the permeation process reaches equilibrium. And the TDS of pure water and concentrated water is almost unchanged.

Base on the above features, the large-capacity filter max TDS value will reach half of the input TDS value. It is the reason for the higher TDS when starting up. For these filters on the market, their capacity is at least 400 gallons.

Why is it 400 gallons? Because the filter can produce 1 litre of water per minute. It meets the national standards, more significant than 0.8 litres/minute. And it meets consumers’ daily consumption.

For other filters than 400 gallons, the difference lies in the larger output capacity. It brings a better user experience.

With fast production speed, this filter no needs a storage tank. Of course, there is no need for post-activated carbon. It solved the bacteria mentioned above and nitrite over-standard problems.

It seems to be a perfect way of technological improvement and innovation. It brings new topics to the quiet water purification market sales. Many manufacturers have successively launched 400G, 800G, 1000G and even higher capacity filters. But, the actual situation is new problems are coming.

The problem of "residual water" has occurred.

The residual water means the first “purified water” from the faucet in the morning. And this “purified water” is not freshly made. But the water that has penetrated through the RO membrane overnight. It should also be pure water.

But, because of two-way permeation of RO, the wastewater can slowly diffuse to the pure water. If the wastewater has more heavy metal ions, the pure water’s heavy metals will exceed the standard. And the water quality and taste will be significantly affected.

Due to the large-capacity, the amount of residual water is not small. It has become a fatal flaw in the actual use process.

Poor user experience

Consumers will encounter the problem of lodging water every time they use water. With a different time between shutdowns, it will generate different volume & TDS residual water.

Thus, manufacturers cannot give an accurate response. And consumers cannot determine how much water must be released. They can keep the TDS value of the effluent within a safe and appropriate range.

Even if you rigidly set a specific time, you have to drain some water every time you use it, and you have to wait a particular time. This kind of experience is difficult for consumers to tolerate.

If consumers knew the TDS of residual water might reach half of the input water, many would change the choice.

Significant increase in the purchase and use costs

Compared with the 50G, the 400G filter cost must increase by at least 50%, and the price will naturally rise. 600G, 800G, or even 1200G pure water machines have higher prices.

For matching with larger RO membrane, we need to increase the capacity of other filters. In this way, you will spend more for the replacement.

For the water consumption of a standard family, a 50G pure water filter has many surpluses. For those filter above 400G, it is using anti-aircraft artillery to hit mosquitoes. It is a massive waste of resources. From this point of view, it is not worthwhile for consumers to buy such equipment.

The effluent flow continues to decrease.

Take a 400G pure water machine as an example. The water flow rate can reach 1 litre per minute at the beginning of use. But, as the RO membrane service life decays, the output capacity will become smaller. After the winter, due to The temperature becomes lower and the water flow becomes smaller. The unstable water flows and the process also lead to the poor consumer experience.

Protecting the RO membrane, many filters have a startup or shutdown flushing program.

The 50G water purifier is to make a tank full of water and then shut down and rinse once. In contrast, the large filter will flush once even if it only receives a glass of water. It results in a larger amount of wastewater. It will also cause frequent startup of the booster system, high & low-pressure switches. And increase the loss.

Large filter for commercial applications can avoid disadvantages while taking advantage.

What do consumers need?

For product manufacturers, all technological improvements and innovations must benefit consumers. Only when considering problems from the perspective of consumers and solve them. The products stand the test of the market.

For water filter, we can tell whether they are genuinely for the sake of consumers from the following:


Since consumers have chosen the filter, they will need the TDS must be within a safe range.

The problem of large filter will go beyond this range.

In the actual use, the quantity and quality of the residual water are different every time. It is impossible and difficult for consumers to have appropriate countermeasures. How much water is discharged? How long is the queue? Both are variables. In this case, many manufacturers’ product manuals also choose to avoid this problem.

Think about it. Every time we turn on the taps, we have to worry about the TDS of the water at the beginning. This unsafe and uncertain feeling will make consumers feel very entangled.

So, although it also has residual water, not much for the small capacity water filter. 

Even this wastewater mixes with purified water; the TDS value is still in a safe range. This kind of result is qualified for safety indicators. Also acceptable for consumers’ psychological feelings. 

Also, you can go to the actual test. A qualified small flux tank water purifier can detect the TDS value of the water at any time. Generally, it can be guaranteed to be within 50, and most of them are within 20.


Drinking water is one of the most frequent events in everyone’s life. And this process must be comfortable.

Having enough and stable flow within a standard time frame when taking water is a critical comfort factor.

For a small filter with a tank, this is not a problem. For different temperature or membrane life, we can have the same capacity as the regular tank pressure. That’s about 2 litres per minute.

For the large filter, the water flow is the largest at the beginning of use. for example, 400G is 1 litre per minute, 800G is 2 litres per minute. Then, as the equipment’s use time is extended, the flow of purified water will gradually decrease. This trend is very uncomfortable for the consumer experience. The water flow is too small, and it will take longer to wait.

The large filter does not bring about the large flow of the use process. It will significantly reduce the acceptance of consumers.


The so-called economy refers to cost performance. And improvement and innovation must help to increase it.

If there is a mismatch between the problem solved and the increase in cost. Cause a decrease of cost performance; there must be a problem with the improvement.

The large water filter relies on increasing RO capacity to replace tank and carbon. It leads to a large increase in the cost of the RO membrane and the matching element. 

From the price of the product, we can tell the price-performance ratio of the product has dropped. We especially compared to the problems solved, and the new problems brought about.

Compared with the traditional water filter, the buy cost and later use price have increased. As a result, it is still relatively difficult to get market approval.

The excess of bacteria and nitrite does not only need a strict selection of technology & materials. But it requests installation hygiene and timely maintenance.

Generally speaking, after two years of use, we should sanitize the whole unit of the water filter. But, few manufacturers have informed consumers of this work. The actual situation is that few people do this.



Based on the above analysis, we can tell that the small water filter will be the mainstream market.

Before solving the problems, the large filter is more suitable for the commercial market.

When some companies promote large filters, they may not understand the real needs of consumers. Or it may be a false proposition—the gimmick effect of water marketing and promotion.

What consumers need is a good experience and enough value brought by the product. Increasing the flux for “improvement” and “innovation” will only create new problems. And make consumers waste money with a bad experience. This approach is challenging to win the trust of consumers.

If you want to know more about industrial water treatment, please click here.



Please click below to watch the production process of bottled water production.

John Lau.

John Lau.

John Lau, a project manager holding an engineering bachelor's degree, became fascinated with optimizing beverage production equipment during his university days. As an overseas project manager, he firmly believes that educating clients on achieving efficient workflows through customized equipment design is one of the most impactful aspects of his job.

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