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By: Ray Lillback

Where Does All the Water Go?

Today’s water disposal methods require a sustainable evolution.


When you flush the toilet, the water inside seems to disappear—it goes “down there,” wherever that is, and out of your home. When you shut off the shower, and the last pools of water in the tub seep down the drain, you dry off and move on with your day. The used water goes away, and clean, fresh water comes out of the tap. You probably don’t stop to think about where the water goes, but this is a vitally important question. The path our wastewater travels impacts our clean water supply and this supply is critical to public health, vibrant communities and our economy.

So, what exactly is water’s “exit strategy?” Let’s follow the path our water travels as it leaves our homes and explore how centralized and decentralized water systems work. Understanding where wastewater (“used” water) goes and how it is treated helps us understand why we must take greater personal responsibility over how we “treat” the water we use.

Sustainable, healthful, effective water disposal is critical to preserving our water supply.

Water disposal is a multi-step process. The path that used water travels as it goes down the drain, into our pipes and through a treatment system depends on the type of infrastructure in place. The path our water travels following disposal, and its sustainable, healthful treatment, impacts our environment, our water supply—and the availability of pure, clean water for us to drink. Let’s follow the path.


Centralized Water Systems

The wastewater we flush out of our homes, and allow to run down the drain, must go somewhere to be properly treated. If you live in the city, that “somewhere” is a centralized water treatment plant, which may be located quite far from your home. Water must travel through pipes to the treatment plant. While distance makes this system inefficient, the level of treatment that occurs at centralized water facilities is quite advanced, involving primary, secondary and tertiary treatment. Then, treated “used” water is discharged to the surface, to rivers, streams and lakes.

The three-tier treatment process carried out at centralized water treatment plants is important because humans are exposed to the discharged water as it is released on the surface. We swim and fish in surface waters. It is critical that the treated water we return to our environment is as pure as possible.

Primary treatment consists of screening and settling to remove large and heavy solids and flotation to separate oils fats and oils. Secondary treatment is a multi-step process that uses several different types of beneficial microorganisms to digest organic matter and convert it to carbon dioxide, water and nitrogen. At the end of secondary treatment suspended solids are settled out again. Tertiary treatment uses sophisticated physical filtration to remove fine suspended solids. After water passes through this three-step treatment process, it is disinfected and at this point, it is deemed safe and clean enough to return to surface water supplies that we may come into direct contact with.

Imagine how efficient it would be to safely and effectively purify water right in our own homes.

Decentralized Water Systems

If you live in a rural environment or developing area, your water may be disposed of using a decentralized system, where wastewater is collected, treated and dispersed or reused at or near the point of generation. Decentralized systems generally involve a septic tank for preliminary “ settling” of used water. Beneficial bacteria remove some nutrients from the water so it is safe to leach back into soil where additional filtration occurs.

There are a few key differences between centralized and decentralized systems. First, centralized systems treat water through three distinct processes, so water is more rigorously purified before it reaches surface water supplies. Decentralized water systems treat used water one time, using a process that is equivalent to a central system’s “primary treatment” before discharging water back into the soil rather than surface water (lakes, streams).

Exploring Water Recycling

Now that we have a simplified, big picture perspective of the complex water disposal process using centralized and decentralized treatment systems, consider what it would be like if we could eliminate water disposal completely? What if we could simplify the complicated path used water takes today and implement a system that serves not only as a water disposal system, but also as a water supply system? We’re talking about water recycling and bringing more value to the way we treat used water because we can capture used water at the source (our homes) and effectively clean and purify it for reuse as drinking, bathing and other household purposes.

When we think about recycling water at home, we also gain a deeper appreciation for the fact that what we put into our water—including pharmaceuticals that leach into the supply, such as aspirin—must be taken out during treatment. That is not always the case in current municipal systems so our water use affects someone else’s water quality downstream. With the right technology and water recycling, all of these are removed.  That’s another topic we’ll delve into as we explore water quality.

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