Toilet to tap

—By Matthew Blair, PhD student of Civil & Environmental Engineering

As an engineer, scientist, and water using citizen, I prefer the terms direct potable reuse, indirect potable reuse, recycled water, and reclaimed water to describe processes that have different applications and that are scantily described by the toilet to tap mantra. In almost all things, terminology matters. You wouldn’t use motor oil to fry up some French fries, but olive, canola, or peanut oils would do fine. In the same sense, no one in the wastewater treatment industry is expecting people to drink raw sewage, as the toilet to tap narrative may imply.

In fact, what the toilet to tap mantra is missing most is context about what occurs between the toilet and the tap, both in our current water use system and in our wastewater reuse future. Currently the ‘between’ is largely unacknowledged reuse where upstream, treated wastewater is further mitigated by traveling through the environment before it is inevitably treated again for potable purposes. Direct potable reuse systems essentially take out the additional environmental conditioning and replaces it with advanced water treatment systems designed to produce safe, purified drinking water that, in the process, closes the water loop.

A UC Riverside blind taste testing study seems to show that not only do these systems have the ability to scientifically close the water loop, but also the gap of public perception — if we allow it. This 2018 study indicates that people (n=143) have an indistinguishable preference for bottled water and indirect potable reuse water over conventional groundwater based tap water [7].

Proponents of the wastewater reuse movement are not just comprised of blind taste testers and technical expects as west coast craft breweries have become some of the most outspoken champions of the wastewater reuse industry and its public perception. Before wastewater reuse options became available it was (and still is) common practice for breweries to take conventional tap water and provide additional treatments to remove minerals, salts and adjust the water’s hardness, alkalinity, and pH. These additional treatments are used to account for conventional tap waters variability and limits the impact of taste altering compounds, but become unnecessary when dealing with reuse water that has undergone rigorous advanced treatment and is referred to by some as ‘zero water’ that is of the ‘highest possible quality’ [8].

In this sense, as engineers set out to turn wastewater into water, they may have accidentally turned it into wine and begun to change the narrative of a saying that has haunted wastewater reuse projects from the beginning – maybe toilet to tap-house is a more appropriate moniker for the immediate future of wastewater reuse.

A future I am glad to drink to.


Print Friendly, PDF & Email

Leave a Comment