How 'Toilet to Tap' Water Is Made

Researchers gave bottled water, recycled wastewater from the tap, and conventional tap water to 143 participants and asked them to rate the waters without knowing where they came from. . (Photo: People Image Studio/Shutterstock )

Recycled wastewater is safe to drink, but the thought of drinking water that once ran through the kitchen sink or the toilet isn't appealing. However, a recent study conducted by researchers at University of California, Riverside and Santa Barbara City College found that, in a blind taste test, more people preferred the taste of recycled waste tap water over conventional tap water.

For the study, published in the journal Appetite, researchers gave bottled water, recycled wastewater from the tap, and conventional groundwater tap water to 143 participants and asked them to rate the waters without knowing where they came from.

What usually happens to wastewater

Water down the drain
Water that goes down the sink eventually becomes wastewater. (Photo: ML Harris/Shutterstock)

To understand what recycled water is, we first need to understand what usually happens to wastewater and how it's treated. Wastewater is water that comes from residences and non-residences that goes into the septic or sewer system. In your home, it includes household water from the kitchen and bathroom, as well as water from washing machines and rain runoff.

When wastewater goes into a septic system, it's eventually absorbed back into the ground. When it goes into a sewer system, it goes through a treatment process that removes contaminants before being released. Where it ends up depends on state laws and individual municipalities' treatment plans.

I took a look at how the wastewater is treated where I live in Camden County, New Jersey. All sewage wastewater in my county ends up in a central location where solids are removed and then sent to primary sedimentation tanks for 12 to 15 hours where solids sink to the bottom and grease rises to the top. The solids and grease are separated from the water, and the water goes to aeration tanks where it's mixed with oxygen and bacteria. In about four hours, the bacteria consume any organic solids in the water, helping to decontaminate it.

The water is then sent to the final sedimentation tanks where the bacteria have a chance to settle to the bottom so they can be separated from the water. The water moves to chlorine contact tanks where it's mixed with a solution of sodium hypochlorite (the same chemical in chlorine bleach). Eventually it's released into the Delaware River and makes its way to the Atlantic Ocean.

In the big picture of the water cycle, that water can eventually make its way back to our drinking water, but it doesn't go directly into any water source that is directly used for drinking. The recycled water in the study was created using indirect potable reuse technology, a method used to treat wastewater with the intention of sending it back into the drinking water supply.

Direct and indirect potable reuse

Wastewater can be added to the drinking water supply through a direct potable reuse method or an indirect potable reuse method, according to Environmental Health. Both of these methods are sometimes referred to as "toilet to tap."

In the direct potable reuse (DPR) method, wastewater is highly treated with advanced processes and sent directly back into the potable distribution system. In the indirect potable reuse (IPR) method, after the water has been highly treated, it's blended with the water in an environmental buffer like an aquifer or a reservoir and then makes its way into the potable water supply.

Toilet to tap to drinking glass

In drought-ridden California, there are already six state agencies that use wastewater that comes from an IPR source, according to the University of California, Riverside. Studies show that this water is completely safe to drink, but that doesn't mean people are going to happily pour it in a water glass.

The researchers from the California colleges hoped that by showing that IPR-treated tap water tastes the same as groundwater tap water, they could make this recycled water more appealing. They were surprised when the study found that the IPR-treated tap water was rated as good as bottled water and better tasting than groundwater tap water by many of the study's participants.

After tasting the water in unlabeled cups, participants were asked to rank the samples on a scale of one to five for taste, and also to rank them in categories like texture, temperature, smell and color. Researchers also took into consideration participants' personality traits.

For the sake of the study, participants were referred to as either having "openness to experience" or "neuroticism." Those who were more nervous and anxious preferred the IPR and bottled water over the mineral-rich groundwater tap water. Those who were open to new experiences rated the water from the three sources about the same.

By highlighting the similarity in taste between IPR water and bottled water, researchers hope it "may make consumers more amenable to drinking recycled wastewater," particularly women who have higher "disgust reactions" and make most consumer purchasing decisions.