How to choose a good reverse osmosis water filtration system

The RO water filter is currently the best filtration device among household water filters. The principle of reverse osmosis in a water filter works as follows: When the same volume of dilute solution and concentrated solution are respectively placed on both sides of the container, it is separated by a semipermeable membrane. The solvent in the dilute solution will naturally pass through the semi-permeable membrane to the concentrated solution. Then the side of the concentrated solution is higher than that of the dilute solution, forming a pressure difference and reaching the equilibrium state of osmosis, known as the osmotic pressure. If a pressure greater than the osmotic pressure is applied to the concentrated solution side, the solvent in the concentrated solution will flow toward the dilute solution, and the flow direction of the solvent is opposite that of the original infiltration direction. This process is called reverse osmosis. Through this mechanism, RO produces pure water and waste water during the process of filtration. The former is for direct drinking and the latter generally flows down the drain.

The RO pore size is 0.0001μm—one-millionth the size of a human hair and one-five thousandth that of bacteria and viruses. It is not visible to the naked eye. Therefore, only water molecules and some mineral ions can pass through (by the principle of ion unprofitable orientation). Other impurities and heavy metals are drained from the waste water pipeline. It removes 99% of harmful substances in water and reduces TDS by at least 90%, solving the limescale problem for your family.

Based on the filtration efficiency, products can be divided into two categories: tank RO systems and tankless RO systems. The RO system with low-filtration efficiency requires a storage tank for normal water filtration and use. At present, tank RO system brands include Apec and Ispring, belonging to the first generation of the water filtration industry. The tankless RO systems are new arrivals, and their brands are less common on the market at present.

Types of Reverse Osmosis Systems

Traditional reverse osmosis system with tank

As shown, the first-generation RO system is generally equipped with a pressure tank, producing 50GPD or 70GPD of water each day. Generally, there are five filtration levels. The first level is the PP filter, the second and third levels are carbon block filters, the fourth level is the RO filter, and the last level is the granular activated carbon filter. Each filter level is connected by pipelines and quick connections. The waste water ratio is 1:3, i.e., three cups of waste water for every cup of pure water. In addition, to ensure water flux, the first generation of RO systems requires a storage tank for filtered water. Therefore, once the filtered water in the pressure tank is used up, it takes another 30 minutes before the water can be used again.


1. Cheaper, from $200 to $300.

2. Relatively lower cost for filter replacement.


1. The storage tank may breed bacteria after being used for a long time. It causes secondary pollution and results in a bacteria value that exceeds the standard for pure water.

2. There are too many connections in the RO pressure tank, resulting in leakage complaints from customers.

3. Filter replacement is complicated and requires special tools. There is no filter life reminder, so filtration efficiency and performance may decline. The water quality can also be influenced if the filter is not replaced in a timely manner.

4. The waste water ratio is 1:3, which means that a lot of water is wasted. The actual waste water ratio usually far exceeds the value claimed by the manufacturer.

Tankless reverse osmosis system

A tankless RO system has no storage tank and comes in a variety of new designs. In appearance, the frame is smaller and the filter is bigger, while the filter performance is improved. In function, it is equipped with such systems as a filter use life reminder, a TDS indicator, smart flushing, and leakage prevention. In terms of structure, it generally adopts integrated waterways, reducing water leakage. Filter replacement is easier owing to the filter throwaway design. In terms of performance, the filtered water can reach 400~500GPD. The waste water ratio is 1:1, saving a lot of water. The tankless RO system has no pressure tank, which prevents bacteria from breeding. Moreover, the tankless RO system adds an internal pump to realize real-time water filtration—no more waiting for pure water.


  1. Composite filters, efficient filtration.
  2. No secondary pollution.
  3. 1:1 low drain ratio, which saves water.
  4. Integrated waterway, which reduces the risk of water leakage.
  5. Filter life indicator, allowing you to replace the filter on time.


1. More expensive than the tank RO.

2. Electricity is needed.

Factors to Consider When Buying a Reverse Osmosis System

1. Family members: If your family has more than three members, you should choose an RO system with a large water filtration capacity that can meet your needs at any time.

2. Budget: If your budget is relatively low, you should choose the tank RO system. However, a tank RO system will waste a lot of water, which will affect your water bills. if you live in California, you will want to choose a product with a low waste water ratio.

3. Under-sink space: If you have insufficient under-sink space, you should choose a tankless RO system, as it takes up less space.

4. Water quality: If you have high water quality requirements, you can choose the RO system with a filter use life reminder and water quality indicator.

5. RO membrane: The core component of an RO system is its membrane. It is suggested that you use a DOW or GE membrane.   

6. UL certification: An RO system with a large water flux will be equipped with pumps and connected to the power supply. Please choose products with UL certification, as there may be electricity leakage in a humid environment.

7. Large water flux: Choose the RO system with a large water flux if you want to connect it to the refrigerator dispenser or coffee maker, or if you want to use pure water for your fish tank.

8. Office use: For office use, you should choose an RO system with large water flux, which not only provides better water quality but is also cheaper than mineral water.

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