How To Add A Post-Activated Carbon Water Filter To A 3-Stage Water Filter?

Water from central water sources like a private well or treatment center usually contains different impurities that make it unsafe to use. Filtering the water before using it is the way to make it safe. The post-activated carbon filter is one of the many filtration systems you can utilize to purify water. It offers a high-efficiency level since it is used in a multi-stage filtration unit.

If the water contains a lot of contaminants, a full-fledged cleansing system is vital to remove them. Since the pollutants will likely be in different sizes, using more than one filter type becomes necessary to ensure complete removal.

This piece shows you how to install a post-activated carbon filter to a multi-stage filtration unit, specifically a 3-stage system. You’ll also learn about post-activated carbon filters and why they’ve become popular.

Understanding 3-Stage Water Filter Units

Multi-stage filters involve the combination of more than one filter to purify water filled with a high impurity level. A 3-stage filter unit contains three different filters that clean water in stages typically based on the sizes of impurities.

Components of a 3-Stage Filter

A sediment filter is typically the first in such a system, as it removes sediments and large particles from the water. They have the most prominent pores, which means tiny impurities will easily pass through them. However, their tendency to stop large particles is of great importance when decayed matter and particles are in the water.

The components of the latter phases of a 3-stage are not fixed but vary based on your water content, as some second-stage filters will require a carbon cleanser and reverse osmosis at the end. Other systems have the carbon filter as the final stage, but generally, carbon is common in the second and third levels.

In this article, we’ll focus on systems that use activated carbon as the final level of a 3-stage filter unit. Removing impurities in phases ensures a wide variety of pollutants like sediments, minerals, chlorine, and more are eliminated.

Post-Activated Carbon Filters

Post-Activated Carbon Filters

Activated carbon filters are carbon cleansers with better adsorption qualities, usually due to increased surface area. Typically, the carbon comes in granulated (GAC) or powdered (PAC) forms, ensuring more time in contact with water and, ultimately, more efficiency.

When an activated carbon is utilized at the end of a multi-stage filtration system, it is known as a post-activated carbon filter. They work after other filters have removed more significant impurities in the water.

Here are some advantages of using a post-activated carbon filter:

  • Improving the quality of drinking, bathing, and cooking water
  • Removing foul odor and taste in the water
  • Easy to install and maintain without professionals
  • Eradicates chlorine and chloramine from the water

How to Select The Correct Post-Activated Carbon Filter

How to Select the Correct Post-Activated Carbon Filter

Before going ahead to see how to install the filter, it is vital to understand how to pick the right post-activated carbon filter for your 3-stage system. In making this decision, here are some factors to consider:

1. Contaminants The Filter Can Remove

The contaminants activated carbon can remove vary from model to model, so it is best to consider the impurity you want to remove and the pollutant the filter can remove. The activated carbon you chose should have the capacity to remove the impurities in your water.

2. Size of Filter And Compatibility With Your 3-Stage Filter

The size of the granules will affect its efficiency, so you want to consider the filter size before selecting the correct activated carbon. Here, the smallest filter size does not necessarily mean the best, as you require a fitting size. You should also consider the activated carbon’s compatibility with your 3-stage system. Incompatible carbon will result in poor efficiency or sometimes complete inefficiency.

3. Lifespan of Filter

Carbon filters have varying lifespans ranging from a few months to a few years. Consider the right fit and how long you expect to use the filter. A longer lifespan often coincides with higher costs, so keep this in mind.

4. Maintenance Requirements

Good activated carbon filters must have a high maintenance strength that prolongs their lifespan as you keep it in good condition. It should also be easy to maintain without the need for complicated processes. Choose a system with straightforward maintenance procedures.

5. Cost

Carbon filters vary based on models and manufacturers with different prices. Select the carbon within your budget that gives you the most value for money, including a good lifespan and easy maintenance.

Step-by-Step Instructions to Add a Post-Activated Carbon Filter to Your 3-Stage Water Filter

Step-by-Step Instructions to Add a Post-Activated Carbon Filter to Your 3-Stage Water Filter

Installing the filter is the next step after choosing the most suitable activated carbon for your 3-stage filter. The process is uncomplicated if you already have the first two filters installed in the 3-stage unit. Here are steps to follow to add this to your under-sink filter:

Step 1: Shut off The Water Supply

For an under-sink filter, the water supply line should be under the cabinet, where you may find hot and cold pipes. The filter should be connected to the cold water line, so you should turn off the cold water using the attached regulator.

Turn the water regulator on the cold water line anticlockwise till it stops. It is vital to relieve the pressure in the pipe before opening any valve, and you can do this by opening the sink faucet and allowing the water to run out.

Step 2: Locate The Installation Point

For a new 3-stage filter installation, find a suitable location under the sink with enough space for the large filter. If you already have the system installed and only looking to add the activated carbon, check under your sink to find the setup.

Clean the sink area to give you access to the spot with a bucket under the filter unit to collect any water droplets. You may also need to place a towel for good head support as you lay facing up while adding the activated carbon.

Step 3: Add The Activated Carbon

A 3-stage filter unit will already have a housing system to accommodate three filters, making adding the post-activated carbon effortless. Before you proceed, you want to ensure the O-ring is firmly in place to prevent leakages.

Put the filter into the filter housing and align the activated carbon filter thread to the filter housing. Hand-tighten the housing by turning it counterclockwise. Complete the addition by turning the housing a few times using a wrench; however, you want to ensure you only fix it snugly to avoid breaking.

Step 4: Connect to The Water Line

For a new filter unit installation, you must connect the system to the water line by fixing the inlet and outlet hoses. The unit will typically show clear markers for the inlet and outlets, so it’s easy to spot. If you already have the 3-stage unit installed, skip to the next tape; otherwise, attach hoses to the adapters and seal them with adapter clips to take water in and out of the filtration system. While cutting the hose, avoid slants, as this may lead to leakages.

Step 5: Check For Leaks

After the installation, checking for leaks is the final step, with the various attachments raising the possibility of a loose connection. Slowly turn on the water connector so water can flow through the filter while paying attention to any leaks.

Leaks around the water housing thread often relate to poor line or O-ring alignment. In contrast, leaks around the adaptors may be due to a badly cut hose or weak attachments. For a newly installed system, allow water to run through the filter with the faucet open for about five minutes. The process is called flushing and removes particles and gases from the filter.

Maintenance Tips For Post-Activated Carbon Water Filter

To prolong the lifespan of your post-activated carbon filter, here are some simple maintenance practices to imbibe:

  • Clean Filter Housing: ensure the filter housing is always clean while also sanitizing it regularly to stop the growth of mold and bacteria
  • Change the filter cartridge: replace the filter cartridge immediately when it is worn out. Careful observation of a change in water quality will show you the best time to replace the filter cartridge.


Post-activated carbon water filters are end-stage filters in a multi-stage system and offer improved water quality as they work to remove chlorine, heavy metals, and chloramines. Adding this filter to a 3-stage filter unit can be done in an hour or two by following the five steps process.

Single-stage filters may not be efficient in getting purified water as their effectiveness is limited. Enhancing your filtration system using a post-activated carbon water filter allows you to enjoy clean drinking and cooking water in your home.