Tank vs Tankless RO Water Purifier – Which is Better?

There are two types of household RO water purifiers on the market, namely with a tank and without a tank. As the name suggests, the water purifier with tank stores the filtered water in a self-contained airtight tank for easy drinking at any time;  The tankless water purifier uses an advanced filtration mechanism to realize the pour and drink without waiting. Consumers make their decisions based on which is better after comparison. Let’s talk about the advantages and disadvantages of the tank and tankless RO water purifiers so that give some suggestions for those who are ready to buy a RO water purifier.

First of all, we must know what an RO system is and how it works.

RO is the abbreviation of "Reverse Osmosis". By applying pressure to the RO membrane, the osmosis phenomenon is reversed. The water molecules enter the low-concentration solution from the high-concentration solution to obtain pure water. Therefore, the core part of the RO System is the RO membrane. As the core of RO water purifier, the RO membrane is the most expensive to replace later. The RO membranes are divided into many types according to the amount of water produced. Take HID's household RO membrane for example, there are 50GPD, 100GPD, 200GPD, 400GPD, etc. RO membranes with different water production volumes have different prices, usually, 400GPD RO membranes are several times the price of 100GPD. Because the filter element in the RO water purifier needs to be replaced frequently, so you must first know the replacement cost of the water purifier filter elements before buying the RO water purifier.
You can refer to this article to understand the filter element replacement cycle：https://www.rotec-hid.com/news/how-often-replace-reverse-osmosis-membrane

Secondly, how does the RO System work?

At present, most of the RO Water Purifiers on the market have a tank. The raw water is preliminarily filtered by PP cotton and activated carbon and then passed through the water pump. After the pump is pressurized, the water passes through the RO membrane. The RO membrane produces two kinds of water, one pure water, and one wastewater. Wastewater will be discharged and pure water will enter the pressure tank. When the tank is full, stop the water production work, turn on the faucet to fetch water, the water in the pressure tank will decrease and continue to produce water. After the pressure tank, there is post activated carbon to improve the taste.

You may clearly be able to see where the pain points of users of this water purifier are, yes, it takes up too much space.

So a lot of manufacturers have begun to promote tankless RO Water Purifiers.

Wow, it's small and beautiful, it doesn't take up any space, there is no tank for fresh drinking, and there is no problem of secondary pollution from storage barrels that some manufacturers say. Therefore, many users have chosen to spend high prices and extremely high post-maintenance costs (this post-maintenance cost may not be mentioned by the water purifier salesperson) to install a tankless RO Water Purifier.

But HID RO Membrane recommends that you choose a pure water machine with a tank if the installation environment allows it (of course, the tank should be a good brand). The reasons are as follows:

Tankless RO Water Purifiers mostly use reverse osmosis membranes above 400GPD to produce water when the faucet is turned on and stop when the faucet is closed. This leads to a problem-unstable desalination rate. You will find that the TDS value of the water will be higher after turning on the faucet after a certain period of time. It takes a while to reach the normal TDS value. This is because after the faucet is closed, the water pump in the machine does not work. At this time, the pressure difference between the inside and outside of the RO membrane is small and no wastewater is discharged. The water with high concentration and low concentration will undergo normal permeation. At this time, the concentration of the water purification end will increase, and the TDS value will increase.

There are tanks of water purifiers, most of which use 50-100G reverse osmosis membranes. Because the water production speed is slow, it is necessary to store the prepared water in a water storage pressure tank in advance and discharge the water in the tank when the faucet is turned on. After turning off the faucet, the pure water mechanism will fill the tank with water. The advantage of this is that after we close the faucet, the water is still making water through the reverse osmosis membrane, and the pump and membrane are still working. Even if the water production in the barrel is completed, the TDS value of the water will be kept within the normal range due to the pressure in the barrel. Moreover, in the domestic water supply system, the pressure tank can also effectively prevent the occurrence of water hammer. The principle is that the sudden cut-off water flow in the pipeline can be absorbed by the airbag in the pressure tank at the moment of closing the faucet.

Therefore, a good small gallon tank water purifier has stable operation, excellent continuous water production, and low cost of filter replacement. If you are wondering whether it is better to buy a tank with a water purifier or a tankless water purifier, you may wish to look at your home installation environment and consider the maintenance cost before making a decision.

Finally, the pressure tank of the RO Water Purifier can be replaced and is not expensive.