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Toilet to Tap Systems

California has now become the second state after Colorado to pass the rule that will allow wastewater to become drinking water. 

California’s Water Resources Control Board unanimously voted to adopt regulations that will enable water companies to use a process known as “direct potable use” to deliver purified wastewater to residents’ taps. 

Before, because of the negative connotation and general unpopularity “toilet to tap'' had, as well as regulatory barriers regarding the safety and quality of the treated water, the transformative practice of converting wastewater into drinking water was never implemented, even though the technology has existed for ages. 

Now though, under the new rules, the wastewater will undergo thorough treatment to eliminate all pathogens and viruses. The purification process will be so extensive that, upon completion, minerals will need to be reintroduced to achieve a taste and chemical composition similar to that of regular drinking water.

This decision is a resounding victory in a drought-prone state as climate change worsens. 

What used to exist in California was a process called “indirect potable use”, where treated wastewater was released into natural bodies of water, such as rivers and reservoirs, in which they would undergo natural purification processes, before being extracted, treated further if necessary, and used as drinking water. The purpose of this was to take advantage of natural purification processes in order to improve the safety and quality of the water prior to its consumption.

With the new process, the already recycled water would undergo a series of treatment stages, including filtration using activated carbon filters and reverse-osmosis membranes, as well as disinfection using UV light, among other treatment methods. The quality of the water is said to be at the same quality as drinking water, or even better in many cases.

According to David Polhemus, deputy director of the State Water Board’s Division of Drinking Water, “this will be by far the most well-treated, highest-quality water served to the public”.  By implementing these new steps, not only will energy be conserved, but the environment will also receive the benefits. This approach effectively decreases the amount of treated effluent discharged into coastal waters. Additionally, incorporating wastewater as a water source, rather than only relying on reservoirs and local supplies, will contribute to bolstering the overall state water supply during periods of drought. 

During a study period from 2001 to 2004, it was determined that we could replace a monumental 81.7% of potable water (regular drinking water) with recycled wastewater. This means that for every unit of recycled water used, it effectively prevented the consumption of 0.817 units of potable water.

The implementation of the regulations will unfortunately not occur immediately as they are required to undergo a final review by the Office of Administrative Law before being put into effect, which is expected to take place in the upcoming summer or fall. Once the new regulations are finalized in the upcoming year, water companies will have the opportunity to submit project proposals for approval by the board. It is important to note that the establishment of the first facilities is still a few years away.


Author links open overlay panel Jason Maier a, a, b, Highlights•Recycled water can be used instead of or in addition to potable water.•Quasi-experimental methods can be leveraged to estimate displacement.•The two-way fixed effects model is used to estimate displacement of potable water by recycled water in , & AbstractRecently. (2021, October 6). How much potable water is saved by wastewater recycling? quasi-experimental evidence from California. Resources, Conservation and Recycling. 

Balarajan, B., & Mossburg, C. (2023, December 20). California wastewater to be recycled into tap water, according to New Regulations. CNN. 

Beam, A. (2023, December 19). Drought-prone California approves new rules for turning wastewater directly into drinking water. PBS. 

Becker, R. (2023, December 19). California approves rules that turn sewage into drinking water. CalMatters. 

California approves recycling toilet water into drinking water - the ... (n.d.). 

Los Angeles Times. (2023, December 17). California prepares to transform sewage into pure drinking water under new rules. Los Angeles Times.

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