From Wastewater to Drinking Water

by | 4.4.2011 at 10:45am | 32 Comments
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Across the globe, 2 out of 10 people do not have access to safe drinking water, and in the U.S., many states face water shortages and droughts. Meanwhile, reports Robert Glennon in Unquenchable: America’s Water Crisis and What to Do About It, Americans use 24 gallons of water each day to flush their toilets—approximately 5.8 billion gallons. What a waste! As the global population continues to grow and climate change results in more water crises, where will we find enough water to meet our needs?

In the U.S., we spend billions of dollars treating water to drinking water quality when we use only 10% of it for drinking and cooking, then flush most of the rest down the toilet or drain. So the growing use of recycled wastewater for irrigation, landscaping, industry and toilet flushing, is a good way to conserve our fresh water resources. Recycled water is also used to replenish sensitive ecosystems where wildlife, fish and plants are left vulnerable when water is diverted for urban or rural needs. In coastal areas, recycled water helps recharge groundwater aquifers to prevent the intrusion of saltwater, which occurs when groundwater has been over pumped.

Photo credit: notcub

The use of recycled water for drinking, however, is less common, largely because many people are repelled by the thought of water that’s been in our toilets going to our taps. But a few countries like Singapore, Australia and Namibia, and states such as California, Virginia and New Mexico are already drinking recycled water, demonstrating that purified wastewater can be safe and clean, and help ease water shortages.

The term “toilet to tap,” used to drum up opposition to drinking recycled water, is misleading because recycled water that ends up in drinking water undergoes extensive and thorough purification. In addition, it is usually added to groundwater or surface water for further cleansing before being sent to a drinking water supply where it is again treated. In fact, it has been shown to have fewer contaminants than existing treated water supplies.

There are a number of technologies used to recycle water, depending on how pure it needs to be and what it will be used for. Here’s how it’s done at the Point Loma Wastewater Treatment plant in San Diego—the city is currently studying the feasibility of recycling water for drinking.

Sewage first goes through advanced primary treatment in which water is separated from large particles, then enters sedimentation tanks where chemicals are used to make primary sludge settle to the bottom and scum rise to the top. Once the water is separated out, 80% of the solids have been removed, and the wastewater is clean enough to be discharged to the ocean. (Though wastewater is a potentially valuable resource, most wastewater produced along our coasts ends up in the ocean.)

In secondary treatment, bacteria are added to the wastewater to ingest organic solids, producing secondary sludge that settles to the bottom.

Tertiary treatment filters the water to remove whatever solids remain, disinfects it with chlorine, and removes the salt. In California, tertiary-treated water is called “recycled water” and can be used for irrigation or industry.

For Indirect Potable Reuse (IPR)—recycled water that eventually becomes drinking water—tertiary-treated water undergoes advanced water technology, then spends time in groundwater or surface water, such as a reservoir, before being sent to drinking water supplies. Advanced water technology first involves microfiltration that strains out any remaining solids.

Reverse osmosis. Photo credit: fhemerick

Next, reverse osmosis, which applies pressure to water on one side of a membrane allowing pure water to pass through, eliminates viruses, bacteria, protozoa, and pharmaceuticals. The water is then disinfected by ultra violet light (UV) or ozone and hydrogen peroxide. Finally it is added to groundwater or surface water reservoirs where it stays for an average of 6 months to be further purified by natural processes. (This is done mainly to assuage public anxiety about drinking recycled water.) Once drawn from the groundwater or reservoir, the recycled water goes through the standard water purification process all drinking water undergoes to meet U.S. Environmental Protection Agency standards.

In fact San Diego is already drinking recycled water because it imports 85% of its water from Northern California and the Colorado River, into which upstream communities like Las Vegas discharge wastewater that is later treated for drinking purposes. Because of recent restrictions on Northern California water and drought on the Colorado River, San Diego, which recycles sewage water for irrigation, invested $11.8 million into an IPR study. The demo project at the North City Water Reclamation Plant will end in 2013. During this time, its Advanced Water Purification Facility is producing 1 million gallons of purified water each day, though no water is being sent to the reservoir.

IPR is more economical for San Diego than recycling more sewage for irrigation would be because recycled irrigation water must be conveyed through special purple pipes to separate it from potable water; expanding the purple pipe infrastructure would cost more than IPR. Recycled water is also less expensive than desalinating seawater. In Orange County, for example, IPR costs $800-$850 to produce enough recycled water for 2 families of 4 for a year. Desalinating an equal amount of seawater would require $1,200-$1,800 because of the amount of energy needed.

To deal with its growing population and salt intrusion into the groundwater, the Orange County Water District in California opened its $480 million state-of-the-art water reclamation facility, the largest in the U.S., in January 2008. It costs $29 million a year to operate. After advanced water treatment, half the recycled water is injected into the aquifer to create a barrier against saltwater intrusion. The other half goes to a percolation pond for further filtration by the soils, and then after about 6 months, ends up in drinking water well intakes. By this year, it’s expected to produce 85 million gallons a day.

Singapore, with no natural aquifers and a small landmass, has struggled to provide a sustainable water supply for its residents for decades.

Photo credit: Jerry Wong

In 2003, it opened the first plants to produce NEWater, recycled drinking water purified by advanced membrane techniques including microfiltration, reverse osmosis and UV disinfection. After treatment, the water is added to the reservoirs. NEWater, which has passed more than 65,000 scientific tests and surpasses World Health Organization drinking water standards, is clean enough to be used for the electronics industry and to be bottled as drinking water. It is expected to produce 2.5% of Singapore’s total daily consumption this year.

Namibia, the most arid country in southern Africa, has been drinking recycled water since 1969. The water reclamation plants produce 35% of the water for Windhoek, the capital city. To date, there have been no negative health impacts connected with the consumption of recycled water.

In 2001, a $55 million water recycling project for water-stressed Los Angeles was scuttled by the public’s revulsion at the thought of drinking recycled water and the term “toilet to tap” was born. Are the public’s fears grounded?

A recent science advisory panel report examined the potential human health implications of “chemicals of emerging concern” (CECs) such as pharmaceuticals, pesticides, and industrial chemicals, in recycled water. The scientists reviewed epidemiological and other studies of recycled water from the last 40 years. While some early studies reported the presence of chlorine disinfection byproducts, the panel noted that treatment methods at that time were less sophisticated. Current methods have been refined and disinfection byproducts have decreased. More recent studies of recycled water found no adverse health effects in populations using recycled water. Though the scientists acknowledged that the effects of long-term exposure (over generations) to CECs and to substances that have not yet been detected are unknown, they concluded that there was “robust evidence that recycled water represents a source of safe drinking water.”

Hopefully public opinion is starting to turn. Dr. Shane Snyder, Professor of Environmental Engineering at the University of Arizona and a member of the science advisory panel, is now studying public perception of recycled water and is finding that “if they trust the utility, the majority of people understand that recycling water is unavoidable.”

The truth is that all water is being recycled over and over—no water on earth is truly pristine. Snyder concludes, “We’re going to drink recycled water one way or another, whether it comes from downstream flow or groundwater. I strongly believe we should to do it through engineered systems where we can actively control the process.”

Columbia Water Center demonstrates research-based solutions to global freshwater scarcity.  Follow Columbia Water Center on Facebook and Twitter

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32 Responses to “From Wastewater to Drinking Water”

  1. Nice article. I like to share a few clarifications:

    1) San Diego’s IPR demonstration project is located at the city’s North City Water Reclamation Plant, not the Point Loma Wastewater Treatment Plant.

    2) Las Vegas treats its wastewater to IPR standards BEFORE discharging it. After treatment it goes into the Las Vegas Wash where it gets “polished” before emptying into Lake Mead. The city also takes its water from Lake Mead at a different location and that water goes to a standard water treatment plant before distribution.

    3) Health implications: studies to date show IPR water to meet or exceed current drinking water standards. Because of concern about “constituents of emerging concern” (CECs) in drinking water (and IPR water) the EPA is now in the public comment phase for a list of 30 new constituents to be regulated under the Clean Water Act. More information about that at: http://yosemite.epa.gov/opa/admpress.nsf/1e5ab1124055f3b28525781f0042ed40/713bc83b19ccad9d85257848006f0aac!OpenDocument

  2. Renee Cho Renee Cho says:

    Thanks for your clarifications, George.

  3. Ashley Sarbacker says:

    Hi my name is Ashley I have a question how much water does a fire station use in a month and how much would it cost to put in purple pipe for about 4 foot ball felds

  4. Renee Cho Renee Cho says:

    Ashley, I am away for 2 weeks. I’ll try to see if I can find answers to your questions when I return.

  5. Renee Cho Renee says:

    Ashley,
    The amount of water used by any fire station varies greatly according to where it is located and what kinds of fires it must fight.

    As for the cost of purple piping, the Equinox Center, a research organization for the San Diego region, estimates that the purple piping infrastructure for IPR costs about $2 million per mile. To answer your question, if each football field is 100 yards and a mile is 1760 yards, purple piping for 4 football fields would cost about $450,000.

  6. richard andrews says:

    does all your rainwater run off from drives, patios gutters ect run into the drains like here in the uk

  7. Renee Cho Renee says:

    Yes, unless people harvest their rain in barrels, most of the water ends up in our drains. And of course, the more the rainwater moves over paved surfaces and the more fertilizer is washed along from lawns, the more chemicals and pollution end up in our water.

  8. Mark says:

    We are very near the point of a global water crisis. Yes, there are isolated examples of communities making great strides in water conservation, but this is a global issue. Policies at the State and Federal levels are more susceptible to the influences of big money. We have a government that for a very long time has not operated for the benefit of it’s people, but rather for the benefit of the large corporations. These corporations spend billions buying legislators to serve their interests. Who do you think these civil servants serve? You? LOL

  9. mike says:

    im glad I leave in the rainy uk over here, however does reverse osmosis not waste a huge amount of water anyway? or do they just keep re-filtering all the membrane rejected water?

  10. Renee Cho Renee says:

    Hi Mike, It’s true that reverse osmosis wastes water – three or more gallons of wastewater are produced for each gallon of filtered water. There are now some zero-waste reverse osmosis systems, but they send wastewater back into the RO system, which makes it work harder and shortens its life.

  11. I really don’t know what the issue is with recycled water.
    There was an article many years ago when i was but a wee lad, that mentioned the water you drink from the tap, has been drunk approx 7 times before.

    Renee, how does the reverse osmosis system work??
    I have visited a stand alone water filtration system here in Brisbane that used a UV filter as the final cleaning agent in treating waste water (Was just clear tubing out in the sun). Effective, but i forget how the rest of the water treatment system worked!

  12. Renee Cho Renee says:

    Hi Adrien, Here is a link to a simple and clear explanation of reverse osmosis:
    http://www.lenntech.com/library/reverse-osmosis/whatisro.htm

  13. mzamo says:

    Renee, id lyk to ask hw many chemicals are used to recycle water and the dosage per litre. Lets say maybe ur reclycling rain,water from the sink,from the washing machine and the bathroom bt nt from the toilet.

  14. Renee Cho Renee says:

    Greywater—leftover water from bathtubs, showers, sinks and washing machines—can be recycled for use in your garden without chemicals. You can learn more here:

    http://greywateraction.org/content/about-greywater-reuse

    Recycling water to drinking water quality, of course, requires a much more complex and sophisticated system, combining filtration and some chemicals.

  15. mzamo dlamini says:

    the reason i needed the information on how to recycle water,is because i wnt to design a h0me water recycling machine,which will recycle water for abwt 2 days than send it to the drain saving water and water bills.but still dont know where to go with it.

  16. Abhilash says:

    Renee, I want to know what are the techniques and instruments available (possibly at low cost)to filter and reuse water from a public wash-basin(installed usually at a railway station or marketplace) .Since, it will require water recycle at a larger scale than a home water recycle system,how will its functioning differ.

  17. Renee Cho Renee Cho says:

    Hi Abhilash,
    Here is a good link that explains the difference between water filtration and purification and provides information about the various methods used to accomplish each.

    http://beprepared.com/article.asp_Q_ai_E_30_A_c2a_E_mt_A_name_E_Water%20Filtration%20And%20Purification

  18. [...] we use only 10% of it for drinking and cooking, then flush the rest down the drain. We should also put more recycled wastewater to use, particularly in urban areas, said [...]

  19. ron fink says:

    My comments are hear say at best, but I understand that the earth is covered two thirds water, one third land. Also, the Navy has been purifying ocean water for years. This article goes into great detail about the process of cleaning the filthiest fluid on earth, while nothing is said of the endless resource of beautiful clean ocean water. Is it maybe because that water doesn’t provide the “brown gold” that sewage provides these Munisapalities for lucrative return as fertilizer sold to the Corporate farm giants. Companies that use water such as that from Orange County should be required to inform purchasers of that fact by labeling information. That goes for Coke, Pepsi, Nestles, and many water bottling companies from Orange County that sell these products to unsuspecting outlying areas. We deserve the right to make the choice, and I choose NO.

  20. Peter Hunt says:

    Water is basic need of life, without it life is not possible. Therefore, we should not pollute the water resources. Gov should implement the law to prevent the disposal of waste material and chemicals in to rivers, lakes, etc.

  21. Demon Lee says:

    I don’t know what all the fuss about drinking recycled water is all about and surprised the article makes no mention of the UK as we have been drinking recycled water for around 100yrs….

    For reference, around 70% of the planet is water, however only 2% is Fresh Water and 1.6% is locked up in the Poles and Glaciers.. this is why there is a concern about the Poles melting as this would ‘de-salinate’ the oceans likely to cause changes in ocean temperatures, currents and weather patterns.

    I am not some ‘Green’ Warrior, but common sense states we need to use water MORE efficiently, stop usinig fresh water in Boilers, Toilets, Washing Machines etc and to recycle as much as we can….

  22. foahom says:

    hello
    I will like to know if it is possible to remove fluoride in waste water by micro organism, and which ones.
    thank you

  23. Peter Gabriel says:

    Damon,

    I think this article is about recycling water from sewage which involves using different technology not available 100 years ago. The bacteria’s found in sewage are just more harmful.

    About recycling generally, unfortunately time to time there is talk about recycling from politicians but UK is far from Germany which for more than 20 years has a more effective compulsory recycling system in place. Honestly I don’t know how many more years are needed to start proper recycling in UK.

  24. With proper water management, the problem of its wastage can be solved. I suffered from this problem in my house until I got in touch with the quality aeration system installers. When logged on to http://www.atlanticdiffusers.com, their depth of knowledge made me realize that with adequate installation of proper equipment of aeration systems, I could save a lot of water.

  25. Tom Watson says:

    Well Im in Grade 7 and i think this is a very useful website! thanks I had to do an assesment about making Dirty water into safe drinking water O_O anyways thanks again! :)

  26. Tom Watson says:

    Oh and by the way:

    Greywater is water from your bathroom sinks, showers, tubs, and washing machines. It is not water that has come into contact with feces, either from the toilet or from washing diapers.

    Greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products. While greywater may look “dirty,” it is a safe and even beneficial source of irrigation water in a yard. If released into rivers, lakes, or estuaries, the nutrients in greywater become pollutants, but to plants, they are valuable fertilizer. Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system, thereby reducing the chance that it will pollute local water bodies. Reusing greywater for irrigation reconnects urban residents and our backyard gardens to the natural water cycle.

    The easiest way to use greywater is to pipe it directly outside and use it to water ornamental plants or fruit trees. Greywater can be used directly on vegetables as long as it doesn’t touch edible parts of the plants. In any greywater system, it is essential to put nothing toxic down the drain–no bleach, no dye, no bath salts, no cleanser, no shampoo with unpronounceable ingredients, and no products containing boron, which is toxic to plants. It is crucial to use all-natural, biodegradable soaps whose ingredients do not harm plants. Most powdered detergent, and some liquid detergent, is sodium based, but sodium can keep seeds from sprouting and destroy the structure of clay soils. Chose salt-free liquid soaps. While you’re at it, watch out for your own health: “natural” body products often contain substances toxic to humans, including parabens, stearalkonium chloride, phenoxyethanol, polyethelene glycol (PEG), and synthetic fragrances. (to learn more about what’s in your products, go to the Cosmetic Database and see how they rate for toxicity) :)

  27. Mollie Brown says:

    I could find no references to recycled water for over 100 years in the UK, as Demon insists. Sites supporting this would be useful. I do not think the UK is ready for Direct Potable Use of recycled water. 100 years ago, there were few beneficial treatments for sewage effluent, so would like to know what Demon’s basis for his assertions are.

  28. Julien-Félix Carrier says:

    What goes around comes around…

    More research is required concerning the effects of antibiotics, hormonal products, and any chemicals susceptible to bio-accumulate or mimic hormones.

    As it stands now, they are released in sewage waters and end up in our rivers, lakes and oceans, then served back to us when we consume fish and seafood. Current municipal treatment chains are’nt designed to extract these chemicals (of which there are too many to come up with a single process) from used water.

  29. vicky says:

    what is procedure of wastewater to the drinking water.. and where is the plant in nashik,maharashtra

  30. Diya says:

    There is a good idea from waste water to drinking water and is there any procedure that how can we covert it in drinking water at home?

  31. Renee Cho Renee says:

    Hi Diya,
    Here is a website that has information about do it yourself water recyling resources:
    http://www.builditsolar.com/Projects/Water/Water.htm#Grey
    I would not try to recycle greywater to drinking water quality yourself, however, because there are stringent drinking water standards to protect your health.

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