What Is Recycled Water, and Can It Help Solve Water Scarcity?

Alyssa Naigan
Nov 2, 2021 · 4 min read

By Milena Raeber

When you hear the term “recycling,” you probably think of municipal recycling — paper, glass, cardboard, and so on. But water can also be recycled, although through a very different process.

Recycled water, also called reclaimed water, is blackwater that has been treated to acceptable levels for reuse according to state and EPA guidelines. It typically comes from city sewage, industrial waste, and stormwater, and can be used for environmental restoration, irrigation, and industrial processes.

In fact, the latter two are exactly how UCI uses it — about 34% of blackwater produced on campus is actually recycled. UCI’s sewage is sent to the Irvine Ranch Water District Michelson plant nearby, where it is sanitized, and the school then purchases a portion of this water to reuse on campus for landscape watering and other purposes.

In 2017, UCI announced a project that swapped out the water in the central cooling plant — which previously had been potable water — with recycled water, estimating it would save about 80 million gallons of drinking water a year. The project was finished in 2018, and the cooling system currently runs on recycled water, reducing UCI’s consumption of potable water.

Several buildings on campus, such as the Anteater Learning Pavilion and the Interdisciplinary Science & Engineering buildings, also have dual plumbing. Dual plumbing involves laying down separate pipes for recycled water and potable water, instead of mixing them (which would be problematic, since recycled water typically isn’t good for human consumption). Though the campus buildings aren’t actively receiving reclaimed water yet, the dual plumbing will facilitate the transition and use of recycled water when a steady source becomes available.

Recycling water gets trickier when the end goal is potable use, rather than practical use. Two methods of recycling water for drinking have emerged: indirect and direct potable reuse. The indirect potable reuse (IPR) method involves adding treated wastewater to a natural drinking water source (which acts as an environmental buffer, e.g. rivers, groundwater aquifers, lakes, etc.), then sanitizing that later to be potable water.

For example, Orange County’s own Groundwater Replenishment System receives treated wastewater received from the Orange County Sanitation District, which is further processed with microfiltration, reverse osmosis, and ultraviolet light, then released into water basins (the environmental buffer) to ultimately become drinking water. Quite a few IPR systems like this one are currently in operation.

In contrast to IPR, direct potable reuse (DPR) lacks an environmental buffer. It involves channeling treated wastewater directly into drinking water systems, which is why it’s also known as toilet-to-tap or flush-to-faucet. This method of recycling water is more complex than IPR because of the absence of the environmental buffer, and not as widespread or regulated. Currently, California is in the process of establishing sanitary criteria for DPR-processed water.

However, as with any water system, there are risks and gaps in knowledge in water recycling. Few systems are in place to reclaim grey water, which is the relatively clean water from household appliances like washing machines, showers, and sinks. This is difficult to do on a large scale because, without knowing exactly what each person washes down the sink, unknown contaminants such as food residue or personal hygiene products can make it harder to treat.

One study also raised concern surrounding certain compounds that can be left over in recycled water, such as pharmaceutical endocrine disruptors (medications that affect hormones, like birth control pills), which have independently been observed to have effects in fish. Therefore, rigorous chemical monitoring systems and regulation criteria are needed to ensure the quality and safety of the treated water.

With freshwater sources already being scarce and climate change bringing worsening droughts, potable water has to be conserved more than ever. Switching to recycled water for non-potable uses is a no-brainer — and using recycled water for potable uses, where possible, is beneficial. Opting out of reusing water would mean ignoring a valuable tool to fight climate change; water reclamation won’t be going away, and will likely play a big role in our sustainable future.

Special thanks to Matthew Deines at UCI Physical & Environmental Planning.

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