Innovations in Urban Water Reuse

By Melanie Holmer

Melanie Holmer is the Water Reuse Leader for Brown and Caldwell, a full-service environmental engineering and construction firm. Ms. Holmer also serves as the Deputy Executive Director for the California Urban Water Agencies, a non-profit organization of eleven major urban water agencies that, collectively, serve approximately 2/3 of California’s urban population.

Oct 25, 2018 | Infrastructure, Resources | 7 comments

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Drought, climate change, and overdraft – oh my!

Communities are increasingly turning to water reuse as a tool to bolster water supply reliability in the face of numerous uncertainties. Droughts result in curtailments of surface water allocations that serve as drinking water lifelines to many cities. Just look at this year’s “day zero” warnings from Cape Town, or when California’s governor made a 2015 executive order requiring a 25 percent water use reduction by cities and towns. Communities that rely on groundwater may find their aquifers in a state of overdraft without adequate management or replenishment. In a world filled with uncertainty, many agencies are looking at water in every part of the urban water cycle as a resource that can be put to better use before discarding it.


It’s all One Water

The urban water cycle starts with raw water, moves through drinking water treatment then delivery to homes and businesses. Once used, sewers convey it to wastewater treatment plants, where it is treated to public health standards for discharge to rivers, land application, the ocean, or treated further for recycled water. Some water is purified through advanced treatment processes and used to augment water supplies.

Water is valuable during all parts of this interconnected urban water cycle – there are opportunities at every step to maximize use that benefits the community, economy and environment. Viewing water as a resource and understanding the interconnectedness of One Water allows for innovative solutions to arise. Purified water injected into aquifers to augment water supply can also halt groundwater subsidence or seawater intrusion, providing multiple benefits. Wastewater treatment facilities can produce energy via co-generation to supply some of their energy needs and offset their carbon footprint. Communities may consider alternative water supplies, such as seawater desalination, stormwater capture, or water reuse to increase water supply reliability and resiliency to prepare for the future.



What is Water Reuse?

Water reuse involves additional treatment of wastewater for other uses. Non-potable reuse, also known as recycled or reclaimed water, is suitable for uses such as landscape or agricultural irrigation, industrial cooling, or toilet flushing. Potable reuse involves advanced treatment processes to produce purified water for addition to groundwater aquifers or reservoirs to supplement a community’s water supply.


Drivers for Water Reuse in the Urban Setting

Communities have been employing non-potable reuse for decades, mostly for landscape irrigation. One limitation for non-potable reuse is that the demand is seasonal, with increased need during the hot, dry summer months. While offsetting potable water use during the summer, this seasonally-dependent demand pattern does not maximize the amount of water that could be reused for other purposes throughout the year. Additionally, most non-potable water systems must be built with a separate, purple pipe distribution system. Purple piping are lines designated for recycled water, which is treated to a level suitable for irrigation and industrial use, but not for drinking. This results in a binary pipe network with high capital costs and operations and maintenance requirements separate from the potable water system. Long pipelines are expensive, and cross-connection prevention requirements add complexity to non-potable reuse systems. These limitations and challenges have led to new trends and innovations for water reuse in an urban setting.


Potable Reuse

Because of the limitations and challenges associated with non-potable reuse, many communities are considering potable reuse as a way to maximize a precious resource before they discharge it to a river or the ocean. Advanced treatment processes such as reverse osmosis and advanced oxidation processes have been demonstrated in California for almost two decades to provide purified water for injection to groundwater, as a tool to stem the tide of seawater intrusion and to augment drinking water supplies. An example of this would be the Soquel Creek Water District, whose primary focus right now is to protect and replenish an overdrafted groundwater basin from seawater intrusion. The District’s Pure Water Soquel project is planning to use advanced water purification methods to purify recycled water for replenishing the groundwater basin and protecting against seawater intrusion. The project would help increase the sustainability of the District’s groundwater supply, upon which it currently relies for 100 percent of its water supply, reduce the degree of overdraft conditions in the District’s groundwater basin, protect against and aid in preventing further seawater intrusion of the groundwater basin, and promote beneficial reuse by reducing discharge of treated wastewater to the Monterey Bay National Marine Sanctuary. Brown and Caldwell is working with the District as program manager as the project moves through technical feasibility and environmental review.

In parched Southern California, where the majority of their water supply is imported, potable reuse allows communities to strengthen water supply reliability and lessen dependence on imported supplies. Some states are developing regulations to allow purified water to be introduced immediately upstream of a drinking water treatment plant, otherwise known as direct potable reuse (DPR). As advances in treatment technologies continue, there is greater possibility for incorporating potable reuse as a viable water supply alternative.


Decentralized Systems

San Francisco leads the way in decentralized, non-potable water reuse systems in the U.S. The headquarters of the San Francisco Public Utilities Commission uses the Living Machine to treat all of its wastewater onsite, producing recycled water to supply water for 100% of the buildings’ urinals and toilets. This onsite system recycles approximately 5,000 gallons per weekday and reduces total water use by about 65%.  Decentralized systems are becoming more popular as an option to keep resources local, earn LEED credits for new buildings and developments, and control water reliability at a small scale.

The California Urban Water Agencies (CUWA) is currently developing a white paper on Decision-Making for Water Reuse Using a Distributed Systems Approach. A distributed systems approach considers regionally optimized supplies, from decentralized to centralized reuse. Decisions could hinge on greenhouse gas production, the regulatory environment, and operational requirements and responsibility. This is an area where both possibilities and the universe of considerations associated with decentralized systems will continue to be explored.


Innovation Next

Utilities, trade organizations and equipment providers are pushing to innovate urban reuse. Communities may seek expanded applications for water reuse and push for regulatory approval of additional uses, as is the case in Colorado to add more official non-potable uses such as urinal and toilet flushing. Much current research is focused on optimizing treatment processes used in potable reuse applications, evaluating performance of alternative treatment processes, and anticipating needs associated with direct potable reuse. A One Water perspective often spurs innovation by challenging planners and engineers to look beyond traditional institutional silos of the past and recognize value in water, no matter where it resides in the urban water cycle.


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  1. Don’t over sell the purple pipe. Reuse water is good for landscape and perhaps toilet flushing but not for drinking water. This idea is planted by construction firms wanting to sell concrete and steel on a massive scale. There is plenty of fresh clean water on the Earth. Moving it to the need is a better use of building infrastructure. Toilet to tap is just risky behavior with a single point failure of a missing O-Ring causing multiple deaths per occurrence. Zealots tend to go overboard on what reuse should be used for. Even if you went all in on drinking your own pee it is a small fraction of the water consumed by the public. Engineering and construction firms need to dial it back for the safety and health of all.

  2. We are planning to build a brand new green and sustainable city, and recycle everything sustain-ably.
    What’s the best way to recycle water, safely and cleanly back to the homes, without waste?
    Your response will be appreciated.


    • Where is your location? There are various approaches available, but the climate (precip., seasonal plant growth), water sources (aquifers?), soils/geology, and development patterns (density, green space distribution, etc.) are a few of the factors that will influence the best approach to a cost effective plan.
      Understand that this is a new field so there are not as many well-tested examples as we might like, but the science and knowledge is there.

  3. It is simply not correct that reclaimed and resuse water CAN BE converted to drinking water. Our City just did exactly that, without reverse osmosis.

    Just last month we were awarded an international water reuse innovation award, beating China and projects from 45 other countries. Of the eighteen nominees across six categories, we were the only entity of any kind nominated from the United States. Our winning project is called pureALTA. pureALTA converts reuse water to purified drinking water WITHOUT reverse osmosis, and the water exceeds drinking water standards. Eliminating reverse osmosis drastically reduces the energy used per MGD. The project is fully scalable with the intention that other cities around the world could implement the exact design, scaled to their needs. We currently reuse more than 100% of the potable water that we use because we serve a wide area. In tandem, we built a STEM Education facility that has served 15,000 middle and high school students, so that we can teach our future generations to embrace conservation, innovation, and STEM fields of study. Though we are small in size and population, we are a regional utility – we serve several cities in two different counties. Environmental sustainability and innovation are core fundamentals for us.

    We use our STEM Education program to teach kids about this emerging technology. Here are some of our links:

    STEM Education:


    Project APRICOT:



    Uber Pilot:

    Altamonte Electric Utility:

    Twitter: and

    Our testing shows that pureALTA cleans reclaimed and reuse water to better than drinking water standards.


    Frank Martz
    City Manager
    City of Altamonte Springs

    • “Currently, the purified water is returned to the reclaimed water system, where it is used for irrigation.

      Thus far, the system has produced reliable results. The City treats approximately 28,000 gallons of water daily but could build a full-scale system with the potential to treat up to 500,000 gallons of water per day—about 5 percent of the City’s future daily water demand ”

      The above from your posted information.

      A water transportation system would bring 51,750,000 gallons per day to your city. If your UV lamp were to burn out how much tainted water would a single point failure produce? How many gallons of tainted water would go to homes before the biological tests came back as dangerous? Is that potentially tainted water quarantined while the lab test has time to work? What is the level of female hormones in that water or beta blockers from high blood pressure medicine? If the public has a contagious disease breakout can the water treatment system still maintain healthy water through that several orders of magnitude spike in pathogens? It rains 39 inches there so you should have plenty of water from local rain.

  4. I am very interested in your comments, we have a mayor in litigation for pollution from the plant, spells, the causes of rivers and estuaries with naegleria fowleri and others.
    The authorities in Chile have not made the facilities according to the law and we are putting everything in order legally, however, the next step is to do the best possible and return to have the nature in balance as soon as possible
    Any suggestions and cooperation will be very grateful

    best regards
    Miguel Thauby

  5. What needs your endorsement is on site waste water recycling for a home. It is a given that grey water with modest “treatment” can be used on site at least for irrigation. Since we use drinking water to flush our toilets were we to steam the effluent and collect the remaining waste we would have two byproducts, water (potable ?) and a nitrogen rich soil amendment. In the larger picture we need to capture, clean and cycle our waste waters where water is used and needed. Call for zero waste water discharge into the ocean. Storm water as well needs to be captured on site and used on site before it gets fouled by street pollutants and off site detritus. San Francisco’s living machine is preceded by other living machines in Weston and Ipswich Mass that have been operating since the mid nineties with ongoing refinements.


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