How Do Drainage Systems Work?

As a species we are remarkably successful at harnessing technology to suit our lifestyle. An area in which we particularly excel is that of our home comforts. From a soft bed, convenient lighting and even entertainment, we have engineered ways to make our lives within the home easier and more comfortable. However when it comes to one of the most basic, yet fundamental, needs of our lifestyle, we don’t give it any thought. We use our kitchens and bathrooms every day, but not many of us know how our drainage systems work.

All houses are connected to a central drainage system, but few people have more than a vague idea about what actually happens to bring water into and out of our homes. Most drainage in the home is surprisingly low-tech, relying on gravity to help move used water. The water is divided into two types:

Grey water: Commonly contains non-life-threatening particles such as food, dirt and soap, such as would be used during the course of a shower or dish washer.

Black water: Water which contains hazardous materials to human health and the environment such as bacteria or human waste, such as from a toilet.

Grey water pipes will often have built in traps, these trap areas tilt up or flatten out, usually in fairly easily accessible areas. Traps give plumbers access to the inside of the pipe for easy examination or unblocking in the event of a problem. This could be to retrieve a wedding band or another small but precious item that occasionally vanishes down the drain.

Black water pipes tend to be larger and do not have any traps. Most toilets do have an S-bend at the top of the pipe to ensure that a small reservoir of water is left in the bowl to help with the flushing and cleaning process. After the gush of water provided when the flush is depressed the toilet relies on gravity to sweep the waste away from the home.

Pipes from household drains flow into the sewers, which are usually found under the middle of the street. These sewer pipes join up to larger pipes, slowly working their way to the water treatment plant along a central drainage network. Thus completing the disposal of our waste water, be it from grey or black water.

It is customary for grey water to be purified, cleansed, and recycled back into the water system as it can easily be made safe for use once again and minimises wastage. Black water on the other hand is contained and disposed of. Most of the dirty water, whether black or grey, begins by sitting for long periods of time in still pools, which allows heavy contaminants to fall to the bottom, while lighter substances like soap scum rise to the top.

After this initial separation process the grey water is repeatedly filtered, purified, and cleaned before being reintroduced to the domestic water cycle. The black water stands to remove the solid waste, which is processed and disposed of, while the liquid remnants are further cleaned, before the water is discarded safely.

There is a massive network of pipes and drains safely removing waste water from our homes and carrying it through the towns and cities to treatment plants. It is something of an indication of just how efficiently the system works that most of us never think about what happens to domestic water once we have finished with it.