How does the reverse osmosis water system work?

A reverse osmosis water system is a water purification system that uses a semipermeable membrane to remove contaminants found in the water.

It uses water pressure to force water through a semipermeable membrane where contaminants are flushed into the drain and clean water passes through.

The process is capable of removing 99% of total dissolved solids contaminants in water, including lead, fluoride, heavy metals, and chlorine.

How does the reverse osmosis water system work?

Reverse osmosis systems are available in two types modern and old. Modern model work differently compared to old ones.

In this article, we will discuss how both modern and old reverse osmosis system work.

The old reverse osmosis system is commonly known as the under-sink reverse osmosis system. The modern model includes such as countertop and tankless reverse osmosis systems.

How does the under-sink reverse osmosis water system work?

A standard under-sink reverse osmosis water system involves different stages to filter out contaminants in the water. Each stage uses a specific filter.

The stages include

Stage 1: Include a sediment filter that helps to remove sand, silt, dirt, and rust. The sediment filter protects particulate from getting to the delicate RO membrane.

Stage 2 includes a carbon filter that helps remove chlorine, taste, and odor.

Stage 3 includes the reverse osmosis membrane, which is the heart of the reverse osmosis water system. The RO membrane helps filter out 99% of the total dissolved solids (TDS) found in water. Such contaminants include lead, fluoride, pesticides, mercury, arsenic, hard water minerals, nitrate, and total dissolved solids. At this stage, contaminants larger than 0.0001 microns are removed.

Stage 4: Include a carbon post filter or polishing filter. It helps remove any remaining taste and odor in the water before it gets to the faucet.

Water gets into the sediment filter and all particulates are removed. Sediment protects the RO membrane from particulates that can clog the system. Then it goes to a carbon filter where the chlorine taste and odor are removed. Chlorine can damage the RO membrane.

Both sediment and carbon filters are pre-filters. They help extend the life of the RO membrane.

After the pre-filter, the water goes through a reverse osmosis membrane, which is the heart of the system. At this stage, high water pressure is required to push water through the RO membrane, so the incoming water pressure should be above 50 psi. If below 50 psi, the system will not remove contaminants effectively, leading to low water quality and rejecting more water to the drainage, resulting in high water bills.

To increase the pressure, you can decide to install a booster pump to increase the pressure. Increased pressure helps the system produce high-quality water, reduce water waste, and fill the tank.

You can install a pressure gauge before your RO membrane to know the exact incoming water pressure on your membrane.

After the water passes through the semipermeable membrane, the purified water goes into a pre-pressurized storage tank where it is stored waiting for human consumption. Contaminants are flushed down the drain.

When you open the faucet, the water passes through the final filter called the post/polish filter. The post-filter helps remove any taste and odor the water might have picked up from the storage tank.

Why do you need a storage tank?

The reverse osmosis system treats water slowly. So the whole process takes a long time before it produces purified water.

You need a storage tank that will collect purified water that is gradually treated. Without the tank, you can end up waiting a long time to fill a glass of water or a pot when you open the kitchen faucet. The tank collects water so you can have immediate access to treated water.

Some systems have an additional filter, such as a remineralization filter, that is installed after the post filter. An RO membrane is known for stripping beneficial minerals that our body requires, such as calcium and magnesium.

The remineralization stage helps add those beneficial minerals.

Shop for an RO system with remineralization.

 NameImageTypeWhere to buy
1Express Water Sediment Replacement Filter BlockAmazon
2EcoPure EPW2P Pleated SedimentPleatedAmazon
3iSpring FP25X25 Sediment Filter BlockAmazon
4Reverse osmosis revolution sedimentSpun PolypropyleneAmazon
5Aquaboon sedimentBlockAmazon
6Ronaqua sedimentBlockAmazon
7APEC Water Systems sediment FILTERpleated SedimentAmazon

Other systems have an additional UV filter. A UV filter is the last stage where water runs in UV light before dispensing to the faucet. It helps eliminate bacteria, viruses, and protozoan cysts.

Also, a storage tank can be a breeding zone for bacteria and viruses. Before water dispenses from the faucet, UV light is required to eliminate bacteria, viruses, and algae.

Shop for an RO system with UV light.

 NameImageReplacement filterFeaturesWhere to buy
1Waterdrop N1 Countertop Reverse Osmosis Water Filtration SystemWaterdrop WD-N1-MRO Filter
Waterdrop WD-N1-CF Filter
Pure to drain ratio is 3:1
4 stages
Automatically activated UV light
Buy waterdrop

Buy Amazon
2Express Water Ultraviolet Reverse Osmosis Water Filtration System (ROUV10DCG)6 Month Reverse Osmosis System Filter Set6 stage
100 GPD
Buy Amazon
3Express Water Alkaline Ultraviolet Reverse Osmosis Filtration System 6 Month Alkaline Reverse Osmosis System Replacement Filter SetStages -11
Gallons per day (GPD)-100
storage tank capacity- 4 gallons
Water pressure 40-80psi
NSF certified
Buy Amazon
4Wholesale market Reverse Osmosis Ultraviolet Water Filter System UV Sterilizer RO 19 pcs Replacement Water Filter Set for our 6 Stage UV Reverse Osmosis System6-stage
UV light always on
100 GPD
Buy Amazon
5APEC Water Systems ROES-PHUV75 APEC Water Systems ROES-PHUV75 Replacement set7-stage
1:3 drain water ratio
75 GPD
Buy Amazon
6iSpring RCC7AK-UViSpring RCC7AK-UV Replacement filter11 watts lamp
lamp on always
Buy Amazon
7NU Aqua Platinum Series NU Aqua Reverse Osmosis 100 Gallon Per Day Universal Replacement RO Membrane7-stages
Buy Amazon
8Geekpure Reverse Osmosis Drinking Water Filter System with UV Filter75 GPD Reverse Osmosis RO Membrane
4 Filters Per Set
1:2 drain ratio
Buy Amazon

Standard under sink RO system goes through the above stages.

How does the under sink Reverse Osmosis drinking water system work?

How do countertop and tankless reverse osmosis systems work?

There are modern types of reverse osmosis systems, such as countertop and tankless reverse osmosis systems, that work differently from under-sink systems.

Both countertop and tankless reverse osmosis systems utilize 4 stages (sediment filter, Pre-carbon plus filter, RO membrane filter, and post-carbon block filter), but they don’t have a tank where water is stored.

Water goes through 4 stages of filtering and is filtered faster, unlike the traditional RO system where the process takes longer. You get filtered water right away from the faucet.

Modern systems have a compact design that takes less space, and the water is not stored in the storage tank, which poses a risk of secondary pollution and requires no installation.

The drawback of the tankless and countertop RO systems is that they require electricity to operate compared with the traditional under-sink RO system that uses incoming water pressure.

Watch the video on how the tankless reverse osmosis water system works.

Shop for a tankless RO system.


Watch the video to see how the countertop reverse osmosis water system works.

Shop for countertop RO system

 NameImageTypeWhere to buy
1Express Water FLTWH2045CGS1 Activated carbon block (ACB)Amazon
2Express Water Whole House Heavy Metal Water Filter SetGranular activated carbon (GAC)Amazon
3Express Water Whole House Anti Scale Filter SetAntiscaleAmazon
4Express Water FLTWH2045K Kinetic Degradation Fluxion Replacement (KDF) Kinetic Degradation Fluxion (KDF) Amazon
5EcoPure EPWHEF Whole Home Replacement FilterSediment (SED) and carbonAmazon
6AquaboonSediment (SED) and carbonAmazon
7Reverse osmosis revolutionSediment, Granulated Activated Carbon &CTO Carbon BlockAmazon
8Reverse osmosis revolution sedimentSediment (SED)Amazon
9APEC Water Systems FILTER-SET-CB3-CBC-20BB 20" pleated Sediment, Granulated Activated Carbon &CTO Carbon BlockAmazon
10Culligan D-250A Cartridge SetCarbon and sedimentAmazon
113M Aqua-Pure Whole House Replacement Water Filter – Model AP917HDCarbon and sedimentAmazon
12Pure Plus Carbon and sedimentAmazon

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