Where does sewage and toilet water go? What happens with POOP after you flush

When you flush your toilet or take a shower, the water disappears. What happens with this and where does it go? Let’s dive in.


Where does sewage and toilet water go? Flushed poop

It depends. In rural areas, people often have a septic system. This is a tank that is located in their garden. The sewage gets processed and cleaned in the tank. The first compartment of the tank deals with the dirtiest sewage. Once this has been processed, it goes to the second compartment of the tank. The remaining sludge gets spread out over a drain field. This septic system has to be maintained and inspected regularly.

Studies are needed before it can be installed. For example, the composition of the soil has to be examined to make sure that the drain field will work properly. Septic tanks can last more than 20 years if they are properly maintained. You can’t flush everything in this tank as you need to make sure that the bacteria can do their job of breaking down the sewage. 

Image by Aunt_Spray via Canva.com

In cities, the sewage is collected from the toilet in the main sewage drain of the house. From there, it goes to the system under the street. Often the toilet water (dark water) and water from the sinks and shower (grey water) are separated as toilet water is dirtier. The sewage of all the buildings in the area is collected and transported to a treatment facility. You can think of this as a big drain that runs to a water management facility.

Gravity is used to transport this water and this means that the drains have to run at a slope. Big machines are used to install these drains and they have to be inspected from time to time to make sure that they are functioning properly. In some cities, it is possible to visit these drains and see what is going on.

Treatment facilities collect the water and clean it step by step. First, the biggest items are filtered out of it. People flush a lot of things that shouldn’t go in the toilet (from wet wipes to trash). Then the water goes in tanks. Bacteria are used to clean the dirt naturally   The sludge is pushed to the lowest part of the tank and then filtered.

Once the water is clean enough, it goes into rivers. The water is tested to make sure that it has enough oxygen and other elements so that it doesn’t affect waterlife. If a mistake is made, a lot of fish can die in a short period of time so this has to be avoided.

These plants are getting more advanced with the introduction of new computer systems and artificial intelligence. This allows them to adjust their processes on the fly. Sometimes the sewage water is dirtier than other times and the processes have to be adjusted to this. Some companies have their own system to treat the water that they use.

Sometimes they use specific elements in their production process and these have to be removed before they can go to the treatment plant. Once the water is in the river, it is transported to the sea or ocean. 

Water treatment facility. Picture by PlumbingInstantFix. All rights reserved

 In some countries, the water is released in rivers without treatment as they don’t have the infrastructure to collect water. They are often still developing this but it can take several decades to dig all the drains and build the plants to process the sewage. This can release plastics and dirt in the water. The Ocean Cleanup is developing systems to clean the biggest pieces out of the water using a special machine. More information about this can be seen in the video below:  

Closing the cycle

Once the water is in the ocean, it evaporates and becomes clouds. This water then rains down on land. This water is combined with groundwater to create the water supply that we use to take a shower and go to the toilet. City water is cleaned before it arrives at our homes. In most instances it is drinkable. If you have a well in your own garden, you have to check the quality of the water yourself.

As you can see, there is a cycle of water. It starts in the seas and oceans, evaporates, and eventually goes into our shower and toilet. From there it drains back to the rivers and eventually the ocean. The process restarts from there. This happens over and over again. This can explain why we have to take care of our water supply and why sewage water is collected and treated. 

More recently there is an effort to collect the rainwater and sewage water separately. This makes it easier to clean the sewage water. If there was a lot of rain, it was hard to collect all the water and treat it properly. In some instances, they even had to release dirty sewage water in the river and thereby reducing the water quality because they were unable to treat all the incoming water. As you can see, we have to take care of the water so that the cycle continues and this is why some countries invest a lot in treating water properly. 

In the past, people used to throw dirty water in the streets. This was dirty and unclean so we have evolved to a more complex system of pipes and ducts. It was a lot of work to dig all the drains. It is actually only quite recently that these systems have been installed. People used to dig a hole in the ground or just throw their waste away. The advent of better sewage systems has allowed us to build modern cities.

To conclude, we can state that our wastewater follows a long trajectory from our home to the wastewater facility from where it goes to rivers and oceans. It can take a few weeks to travel from our home to the river. Think about this the next time you flush! Most people take this system for granted but a lot of things happen in the background. These systems have to be maintained and monitored all the time so people are working every day to make sure that the waste water is being treated properly.