Difference Between Above and Below Ground Drainage

What is the difference between above and below ground drainage? In simple terms, above-ground drainage systems allow us to pass our accumulated rooftop water through a downpipe and gullies. It mainly deals with heavy rainwater, while the underground drains collect our solid and liquid waste from the toilet, basin, and bathtub we use in our houses.

But to give your house longevity, you have to know a bit more than this.

As you’re here, it means you are just one step behind to understand how the drainage system works and what characteristics make one drainage system different from the other.

Stay tuned till the end!

Difference Between Above and Below Ground Drainage

Point Of Comparison  Above Ground  Below Ground  
  Pipe material  Mostly Copper  Plastic, P.V.C., and sometimes cast iron or ductile iron.  
PurposeTo collect rainwater that accumulates on the roof of the house.  To transport the dirty water of toilets, sinks, and basins through soil pipes and waste pipes.  
Destination  Nearest water source (river or lake)  Nearest Waste Treatment Plant  
Treatment Method  No treatment required  Pre-treatment grid chamber, primary treatment, secondary treatment, and disinfection  
Form of structureGutter and downpipesCombined, separated, and partially separated.  

When you build a house, all you think about is the interior designs. But trust me, the most important part of your house is its drainage system. Just a “one wrong step,” and your dream house will be damaged in front of your eyes!

Now that you had a small preview of their differences let’s go down below. Here you will have the above and below ground drainage systems explained.

Pipe Material

First, we will compare the above vs below ground drainage system based on the materials used in the pipes.

Above ground drainpipes have Copper as the core material. Since it exists to carry water, the material should be corrosion resistant. And Copper is 100% rustproof. That’s why it is the perfect choice for making water pipes. Another reason why it is so popular in pipe manufacturing is its ability to bend easily.

But the drawback is that Copper can’t absorb the gas produced in the inner chamber. This can cause an explosion and severe damage to the whole sewage system. Consequently, engineers don’t use Copper in the below-ground section.

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However, underground pipes mostly have plastic or P.V.C. in their body. For hot water lines, CPVC is the better option. These pipes are chemical and corrosion-resistant. But it lacks flexibility. So, you have to install more fittings to connect everything.


The purpose of the above-ground drains is to move the rainwater from the rooftops of the houses. If the water stays on the roof for a long time, it can cause it to corrode. Also, accumulating too much water around the house can cause the groundwater level to rise.

Consequently, that place will have a low ability to withstand floods in the future. To prevent this phenomenon, gutters and open channels or sunken channels were popularized. The purpose of these fixtures is not to let the water accumulate around the house. You should always make sure that the downpipe is releasing the water at least 4 meters away from your house. Otherwise, the ultimate purpose will fail.

On the contrary, the purpose of the below-ground ones is to keep your waste away from you. It deals with all the rubbish your home appliances like washing machines, toilets, bathtubs generate so you don’t have to. The purpose is to recycle this waste and produce drinkable water again.


This is the most noticeable difference between above and below ground drainage systems.

Gutters and downpipes which are the two basic forms of above-ground drains carry water to the gullies. You will find such gullies near your home. It is on the same level as the ground. Passing through the gutter and then the downpipe, water goes underground. Then it is carried to a separate sewage tank. And finally, it goes back into nature without any treatment.

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But that’s not the case for underground drainage systems that carry rubbish water. It has a longer route to travel. First, all the private pipes carrying wastewater from people’s homes connect to a local sewer pipe. Sewer pipe is maintained by the public authority. Soiled water then enters into a water treatment plant using gravity. That’s why these plants are commonly established in a lower region.

 In this case, when an area stays lower than the plant itself, artificial pumps are designed to pump out the waste from the pipes.

Treatment Method

Civil engineers make sure that gutters and sewage pipe don’t mix their liquids along the way. Because rainwater doesn’t require as much attention as wastewater. It is simply carried through the gullies and then released into the nearest water source like a river or lake.

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Unlike rainwater or stormwater, waste in the below ground drainage pipe requires intensive filtration. The soil and sewer pipes dump the waste into a sewage bin. It is then carried to the wastewater treatment plant. The procedure consists of 5 steps.

  1. Pre-treatment: In the first step, all the rubbish is taken out of the water using a bar screen. Now the water is free from objects that could hamper the machines during filtration.
  2. Grit Chamber: Next, the wastewater enters into a grit chamber. Here all the rocks and sands that escape the bars slowly settle out, and chemicals can’t remove grits.
  3. Primary Treatment: A primary clarifying basin uses the principle of settling velocity to remove any particle larger than 10 micrometers from the effluent. The wastewater that comes outside the grit chamber is called effluent. After this stage ends, all the molecules remaining in the water should be organic.
  4. Secondary Treatment: The effluent enters into an aeration basin. The purpose is to degrade the biological components of the water. Thousands of R.A.S. (returned and activated sludge) are a type of bacteria that contributes to this process. To make aerobic digestion easier, a massive amount of air-blowers blow oxygen into the effluent.
  5. Disinfection: In the final step, we have to kill the bacteria we injected in the previous step. Engineers use chlorine, ozone, or U.V. light.

And that’s how the water is safe to drink again or use.

Various Forms

Underground drainage layouts can be of three basic forms. Let’s explain a bit.

  1. Combined below ground drainage system: In this type, both foul and rainwater are dumped into the same sewer. It is the cheapest layout you will find.
  2. Separated below ground drainage system: This is the most economical option in the long term. Two sewers carry two types of water. Foul water is carried to the plan for further treatment, and rainwater is released. The key is that foul and surface water doesn’t mix.
  3. Partially separated drainage system: This is the option when urban areas don’t have enough space to establish two sewers. In a partially separated drainage system, one sewer has two parts that carry two different types of waste and don’t mix.

For the above-ground drainage system, we have gutters and downpipes. Both gutters and downpipes can be of various types. You have to choose the one according to your needs. For example, downpipes come in round and square shapes.

The square one has more capacity to pass water during heavy rainfall. So, if you live in a place where storms and rain is frequent, you should go for this one.

This Video Will Help You Too!

Frequently Asked Questions (FAQs)

What Is Above Ground Drainage?

What Is Below Ground Drainage?

Below ground drainage refers to the transportation of sewage and rainfall water from your home to the treatment plant. All the pipes are buried underground to hide from our eyesight. The chambers are airtight and have a lot of access points. In case you can’t fit your bathroom fixtures with those points, make sure to install a macerator.

Can Soil Pipe Run Over Ground?

Using gravity, soil pipes deliver your solid toilet waste and water to the sewage tank. So yes, they can run overground. Besides, the materials of soil pipes are mostly cast iron or P.V.C. PVC pipes are recorded to perform extremely well in both overground and under-ground plumbing projects.

Can A Sewer Pipe Be Over Ground?

Sewer pipes carry the liquid water waste of your homes and industries to their ultimate destination. The pipes are made of Copper. And according to below-ground drainage building regulations, you can’t install any copper pipe for underground plumbing requirements. Waste in the pipe will produce gas but Copper doesn’t absorb any such substance. It can lead to explosions or damage!


In the end, both of the systems have their own tasks and benefits. You can’t prefer one over the other. Upper ground drainage protects your home structure from damage and groundwater level by throwing the rainwater far away, while the below-ground one manages your sewage waste and sends it to the plant for recycling.

Knowing the details about how your home’s drainage pipes work will eventually help you make the right choices for your house. Hopefully, now you’re quite familiar with the difference between above and below ground drainage system.

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