How an Under-Sink Water Purifier Works

A single-stage under sink water filter works to reduce sediment particles like rust and dirt, chlorine odors and unpleasant tastes in your home’s tap water. It also removes heavy metals like lead.


A flexible plastic tube connects to the cold-water pipe under your sink. From there, a separate second faucet mounted on the sink delivers filtered water directly.

Reverse Osmosis

The heart of an under-sink water filtration system is its reverse osmosis membrane. This process removes a wide range of contaminants, including minerals and salts, from your drinking water at a molecular level. It also reduces chlorine, chlorine odors and other unpleasant flavors, and microorganisms.

A good quality reverse osmosis system has multiple stages of filtration and a large storage tank. The first filter is usually a sediment filter that removes rust, dirt and other larger particles. It is followed by a pre-carbon filter that removes chlorine and other chemicals. The RO membrane then filters out most other molecules that are heavier than water, such as sodium, dissolved metals and other contaminants, while the post-carbon filter polishes the water’s taste.

This stage also allows you to add a specialty cartridge, such as a calcite or alkaline water filter, to increase your water’s pH and provide mineral flavor. Many systems also incorporate a water remineralizer cartridge that replenishes lost minerals.

The reverse osmosis system is a much more efficient option than buying bottled water. Producing bottled water involves a lot of waste, from the plastic used to make the bottles to the gasoline it takes to deliver them to your home. A well-designed under-sink system can produce bottled water quality hydration in your kitchen, reducing waste and eliminating the need for weekly grocery trips.


Pre-filtration removes larger particulate matter from water before it goes through a more detailed filtration process. This is important because large particles have the potential to clog or prematurely exhaust the filter(s) that follow them in the system and reduce their effectiveness.

In addition, removing these larger organic materials prevents them from damaging appliances like washing machines, bathtubs and water heaters. It also extends their lifespan and reduces maintenance costs.

A sediment pre-filter works to eliminate dirt, sand, rust and silt from your home’s water supply. This removes a wide range of mechanical impurities and protects your primary filters from clogging. This reduces the frequency of filter changes and the amount of money spent on maintenance and repairs.

Other common water purifiers include a carbon filter, which removes chlorine and other dissolved chemicals from your water. This protects the more delicate filtration processes that follow it from damage and increases the overall quality of your water.

The importance of pre-filtration is illustrated in the recent water crisis in Flint, Michigan. Several factors contributed to the crisis, including inadequate pre-filtration, which allowed high levels of lead and bacteria into the water supply. For this reason, it’s vital to make sure your water filtration system includes a pre-filter that suits your specific needs. To learn more about the many different types of water filtration systems we offer, contact North Carolina Water Consultants. We serve clients throughout the state, including Matthews, Kannapolis and Cornelius, NC.

Carbon Filtration

Activated carbon filters work to filter out organic chemicals and contaminants that aren’t easily removed by the reverse osmosis or pre-filter. They do this by a process called adsorption, which is when chemicals and other pollutants are attracted to the carbon and held to it. This is because the carbon has so many pores and cracks that the contaminants adhere to it, much like iron filings sticking to a magnet.

These filters are typically placed after the pre-filter and the reverse osmosis stage of a multistage under-sink water purifier. They also can be used as a standalone system to remove certain types of impurities from drinking water. Specifically, they can be used to reduce VOCs (volatile organic compounds), chlorine, chloramines, herbicides, pesticides, fluoride, heavy metals and more. They can be made of granular activated carbon (GAC), powdered activated carbon (PAC), or a combination of the two.

These filters are known for improving the taste and odor of drinking water and removing unwanted chemicals and contaminants from it. They are also great for reducing the presence of cysts and other harmful microorganisms in drinking water. They also have the ability to remove a large number of common contaminants from the water without removing the necessary minerals that your body needs. They have a low cost and are easy to maintain.