Urban wastewater, after treatment to a suitable level, is a good substitute for groundwater or imported surface water for irrigation and other on-farm uses. The California Water Recycling Criteria (encoded in Title 22 of the California Code of Administration) allow 43 specified uses of recycled water—including irrigation of all types of food crops. These criteria include different water quality requirements for irrigation of each type of crop; those eaten raw, those receiving processing before consumption, and those not involving any human contact before industrial processing. These regulations are among the most stringent in the world and have been used as a model for many other countries’ guidelines and water reuse regulations. In California, growers using recycled water meeting the Title 22 criteria have shown over the last 50 years that this practice is safe and economical. Recycled water is also sustainable, conserves energy and provides a significant portion of the nutrients needed by the crops—nitrogen, phosphorus and micronutrients.
Chemical Quality of Recycled Water
Recycled water often contains about 300 to 400 mg/L more salt than does the potable water from which it is generated. Therefore, growers should insist on obtaining periodic water quality data from the municipal agency that delivers recycled water to them. The data should include parameters and constituents of agronomic relevance, such as total salinity (or electrical conductivity), sodium, calcium, magnesium, boron, chloride, sodium adsorption ratio (calculated from the other constituents), nitrogen, phosphorus, bicarbonates, pH, etc. With such data in hand, the grower can (and sometimes should) adjust fertilization and irrigation practices, such as scheduling, depth, and leaching fraction. Such adjustments may be critical under many situations to successful and beneficial use of municipal recycled water.
What can the grower do?
The individual grower can protect him/herself against future droughts, interruptions, higher water costs, and severe water shortages by tapping into the nearest available source of recycled water. Such sources can include:
- Major wastewater treatment facilities of large cities, many of which now are becoming recycled water production facilities,
- Medium-sized wastewater treatment plants serving smaller rural communities,
- Small or package treatment plants serving clusters of residences in isolated areas, and
- Gray water from an individual residence tapped for irrigation of a garden patch that might include food crops (exercising care to avoid exposure of edible portions of the crop to the untreated gray water.
- Tailwater from upstream furrow and flood irrigation practices with their inherent excesses and inefficiencies.
Reclaimed water from any of the first three sources can be conveyed either by gravity of pressure pipe to the farm and reused to free up drinking water. Gray water does not have a significant place in commercial agriculture, because of its relatively small volume and limited applicability. Tailwater reuse is a significant water source for farms where runoff at the end of the furrows is an inevitable consequence of surface irrigation. With laser leveling and highly controlled irrigation practices, tailwater is minimized on the more modern, well-operated farms. Nonetheless, tailwater is a potential water resource and can be captured for reuse.
Proactive use of recycled water by the farmer would involve input by the farmer in the microbial and chemical quality of the delivered recycled water. The level of treatment mandated by regulations is simply a floor—a minimum required quality that would protect the public health. Farmers need water quality that also protects their soils in the long-term use of recycled water. Wastewater treatment plants can change the chemicals they use for various treatment processes if they are given the necessary information and incentives to do so. Thus, growers should insist on a recycled water chemical quality with criteria that will not be injurious to their particular soil, crop, and climatic conditions. Because soils, cropping patterns and climatic conditions vary so much from one location to another, each farmer would need to determine the acceptable levels of these critical parameters for themselves.
Water savings achieved by using recycled water can range up to 100 percent of the demand, depending on the extent to which available recycled water must be supplemented with traditional sources of irrigation water. In some cases, river water or well water is supplemented with recycled water to produce a blend with a lower salinity than that of straight recycled water. Currently, farmers in California use roughly 250,000 acre-feet of recycled water each year for a wide variety of crops. There is significant opportunity to substantially expand the use of recycled water for agricultural irrigation.
The applicability of recycled water for agricultural irrigation is nearly universal. Limitations to its use are similar to limitations applicable to other sources of irrigation water—e.g., salinity, sodicity, presence of specific ions in higher concentrations than allowed in standard agronomic practice. In addition, the level of treatment that recycled water has received determines whether restrictions are imposed on allowed crops or not. Disinfected tertiary recycled water can be used for unrestricted irrigation of all crops, without any limitation on irrigation method employed. For a complete listing of allowed uses of recycled water at different treatment levels, click here.
The greatest hurdle to use of recycled water for irrigation is distance from the source of recycled water. Usually, farms are in rural areas located at long distances from urban centers and their wastewater treatment facilities. And, even if all urban reclaimed water could somehow be transferred to agriculture, the total agricultural demand for water is many times greater than the available supply of municipal recycled water. Thus, farm areas with close access to sources of recycled water are at a unique advantage over others especially in times of drought and in a future that is anticipated to be far more water-scarce in general.
Energy savings with recycled water
The energy used to generate and deliver recycled water is a fraction of that of imported water resources in many parts of the world—especially in Southern California. There, the imported water must overcome a lift of over 2,000 ft, climbing the Tehachapi Mountains, before arriving at the farm gate. Recycled water delivered in those regions has an embedded energy that is less than a fifth of that in imported water. All it needs is a modest amount of energy for treatment and conveyance before it is used for irrigation. This energy differential also translates into a proportionate reduction in the carbon footprint when recycled water is used for irrigation.
Benefits for wastewater treatment plants
Most managers of wastewater treatment systems and their directors are now aware of the important water resource that their treated effluent potentially represents. They are also aware of the environmental impacts of their discharge to the environment. Thus, they are becoming increasingly motivated to find customers for their recycled water. Many public agencies invest huge amounts of resources in laying our infrastructure for distribution of the recycled water to the end users. In California, agriculture represents 40 percent of these end users of recycled water at the present time. The revenue from the sale of recycled water represents another incentive for communities with a significant volume of potentially recyclable water available for reuse. This is usually not a major motivator as the costs of treatment and distribution generally far outweigh the revenue. Therefore, federal and state governments have provided large subsidies to local agencies in recent years, in response to regional water shortages and droughts, to encourage water reuse.
Another major incentive for wastewater treatment plants to recycle their effluent is the upcoming tougher discharge requirements involving removal of minute concentrations of heavy metals and organic compounds through imposition of total maximum daily load (TMDL) regulations. The upper layer of farm soil and its rich microbial population can handle organic compounds that would otherwise be unhealthful if discharged to a surface water body, such as a river, lake or ocean. The soil does this by precipitating, absorbing, adsorbing, digesting, hydrolyzing, or decomposing organic compounds. Therefore, recycling water for agricultural and landscape irrigation is a far superior course of action for society than a high level of treatment for removal of another three or six logs of microconstituent concentration from the water. Even then, someone may ask if the remaining parts per trillion can harm fish or other amphibians in receiving waters.
Significant environmental benefits can be garnered by redirecting wastewater to fields that may otherwise degrade sensitive water bodies. Furthermore, recycling agricultural water can offset withdrawals from surface water, bolstering water flows for fish, other wildlife and plants.
BDOC as a Performance Measure for Organics Removal in Groundwater Recharge of Recycled Water
Produced by an independent advisory panel of the National Water Research Institute, this report compares two water quality monitoring tools for evaluating recycled water used for groundwater recharge. The panel looked at the suitability of biodegradable dissolved organic carbon (BDOC) as an alternative to total organic carbon (TOC) and found that, if properly validated, BDOC can be “a much superior measure of health protection than estimates of wastewater TOC.”
California Department of Water Resource
The CA DWR is the State’s largest wholesale provider of water to agricultural, urban and industrial water users in California. It is highly supportive of using recycled water for all uses allowed by the regulatory agencies. This agency and its sister agency, the State Water Resources Control Board provide significant financial support for recycled water projects throughout the State.
Irrigation with Recycled Water in Santa Clara County
The Santa Clara Valley Water District engaged researchers from the University of California to investigate soil and plant constraints on the quality of recycled water, and propose water qualities and management practices that would enable sustainable use of those waters.
NRCS Technical Guide
NRCS provides a set of key technical resources to guide on-farm water (and other resource) management practices. These include information and recommendations about specific practices related to use of municipal recycled water as they pertain to local areas. Visit the online Field Office Technical Guide (eFOTG) and click through to the map to your county for details. Once there, you can search through practices listed in Section IV of the pull-down menu in the left-hand column of the page. Here, you may also find information about financial support that may be available for implementing these practices. In addition to practice-specific assistance, the eFOTG provides key data to help growers in resource management decision-making, including natural resource information (Section II in the pull-down menu) about local soil (e.g. web soil survey), water, air, plant and animal resources; planning tools for developing resource management systems (Section III); and other useful tools and information.
Review of California’s Water Recycling Criteria for Agricultural Irrigation
Produced by an independent advisory panel of the National Water Research Institute, this report examines the risk of exposure and infection from waterborne pathogens due to the irrigation of a wide variety of food crops using recycled water and provides suggestions to refining the State’s Water Recycling Criteria.
This quarterly publication has been designed to provide a centre point for information on recycling water, summarising the lastest news on recycled water from across Australia and making it readily available to all those interested.
United States Environmental Protection Agency Region 9
USEPA has published an extensive compendium of Guidelines for Water Reuse, providing case studies, international experience and a collection of regulations from the states that have adopted regulations for safe use of recycled water.
WateReuse Association is a professional society of public agencies, academics, and consultants involved in various aspects of water recycling throughout the world. The research arm of this association is WateReuse Foundation. This foundation provides funding for cutting-edge research at the most prestigious universities to continuously improve the state of our knowledge about water reuse.
Water Conserv II is the largest reuse project of its kind in the world. Based in Florida, USA, this project sees 2,737 acres of citrus irrigated with recycled treated wastewater, and recharges local aquifers via rapid infiltration basins. Water Conserv II
The Northern Monterey County has long been water-short, resulting in overpumping of the aquifer, declining of the water level in wells, and seawater intrusion into the local aquifers. Seawater intrusion has resulted in abandonment of many farm wells because of increased salinity levels in the water drawn from those wells. When the possibility of establishing a recycled water service zone became available to the farmers in the 1970s, their first reaction was skepticism:
- would the water be safe?
- would the salinity and salt content be OK for their soils?, and
- would the public continue to buy produce irrigated with recycled water?
An eleven-year pilot project in the 1980s answered these questions in the positive and the needed infrastructure was built to supply the farmers with a distribution network of 45 miles of pipes, 22 supplemental wells, and a coverage of 12,000 acres. Today, this is the largest raw-eaten food crop area in the world irrigated with recycled water, growing strawberries, lettuce, cauliflower, broccoli, celery, fennel, artichokes, and other high-value, intensively grown vegetables. These fields have been irrigated with 13, 000 acre-ft per year of recycled water since 1988, supplemented with well water during high-demand months when the supply of recycled water is not adequate to meet all thee demand on these 12,000 acres.
The Santa Rosa Water Reclamation System comprises 6,130 acres and utilizes 45 pump stations that deliver reclaimed water to the buried pipe and above-ground irrigation systems. A large variety of unrestricted crops are grown in Sonoma County including vegetables, fruits, orchards, and pasture. An initial study of the program was published in 2002, and a report of the Recycled Water Master Plan was published in 2004.
The case study, part of the California Farm Water Success Stories series, explores how Sea Mist Farms and Sonoma County successfully use recycled water for agriculture and describes the costs and benefits from the application of water reuse.
Watsonville is a recent convert to use of recycled water for growing vegetables and fruits (primarily strawberries, comprising 70 percent of all strawberries consumed in the USA). About 4,000 acre-ft per year of disinfected tertiary recycled water is provided to a network of pipelines serving the farming areas in the vicinity of Watsonville. This
project started delivery of recycled water in 2007.
Frequently Asked Questions about Recycled Water
Where does recycled water come from?
Recycled water is wastewater that has been purified through a series of treatment processes. The treatment system can provide this sustainable supply of water for agricultural and many other uses. Most treatment systems utilize three treatment processes in the production of recycled water:
- Primary treatment which removes all debris and inorganic material from the water,
- Secondary treatment which is a biological treatment process where microorganisms metabolize all organic material, and
- Tertiary treatment which polishes the water through filtration, and disinfects the water through the use of chlorine or ultraviolet light.
According to the California Water Recycling Criteria, tertiary-treated recycled water is safe for all human contact, except drinking.
Why are over 250 systems in California producing and distributing recycling water?
First, recycled water is reliable – Even in times of drought when restrictions are placed on the use of potable (drinking) water for non-essential uses like agricultural irrigation, recycled water is readily available. During periods of mandatory cutbacks and water rationing, recycled water can save an investment of hundreds of thousands of dollars worth of commercial landscaping.
Second, Recycled water is competitively priced – Because it’s locally produced, the public agencies can provide recycled water at a per unit rate which is less than the potable water irrigation water rate. Recycled water often costs 80 to 90% of the potable water rate for irrigation.
Third, Recycled water’s nutrients reduce fertilizer costs – Some essential plant nutrients survive the wastewater treatment process, giving recycled water an added benefit. Many recycled water customers have discovered that fertilizer costs are substantially reduced for farms irrigated with recycled water.
What is recycled water used for?
Recycled water is provided for irrigation of farmlands, Homeowner Association common areas, school grounds, parks and golf courses.
Who Benefits from Recycled Water use?
Everyone benefits from recycled water. As the population in California continues to grow from the current 32 million to an estimated 52 million people by the year 2030, so does the demand on our limited water supply. Since our drinking water supply is limited, finding ways to conserve that supply is critical. By using recycled water for irrigation, we can conserve our precious drinking water supply while providing a reliable, growing, and drought-proof source of additional water.
Is Recycled Water Safe to Use?
Yes! Recycled water is made by purifying wastewater. It is given additional disinfection and filtration processes that make it safe for irrigation. Recycled water is carefully monitored to protect public health and safety, and is strictly regulated by the local and state Departments of Public Health and the Regional Water Quality Control Board. It is safely used at hundreds of farms, parks, schools, greenbelts, agricultural operations, and golf courses throughout California. The recycled water pipeline system is separate from the drinking water system.
What Will Happen if An Animal, Such As Horses, Dogs and Cats Drinks Recycled Water?
Recycled water is almost as pure as drinking water. It has been carefully treated and has been disinfected to kill microorganisms. As a result of this treatment, recycled water is perfect to use as a supply for irrigation. Even if you or a pet swallowed recycled water, it should not cause sickness. However, it still contains very small concentrations of some microconstituents and salts that keep it from meeting our strict drinking water standards.
How long has recycled water been used?
Water recycling is practiced worldwide. California has been a pioneer in water recycling for over 50 years. In California there are over 250 water recycling plants in operation. The first wastewater treatment plant built solely for water recycling and reuse was constructed in 1932 in San Francisco (McQueen Plant) to irrigate the world-renowned Golden Gate Park’s landscaping, fill its lakes and provide water for its waterfalls and streams.
Content for this page was originally developed by Dr. Bahman Sheikh, a Water Recycling Consultant. Various others have since contributed content.