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Communication

Achieving Responsible Reclaimed Water Reuse for Vineyard Irrigation: Lessons from Napa Valley, California and Valle de Guadalupe, Baja California

by
Marc Beutel
1,*,
Leopoldo Mendoza-Espinosa
2,
Clara Medina
1,
Jorge Andrés Morandé
1,
Thomas C. Harmon
1 and
Josué Medellín-Azuara
1
1
Environmental Systems Graduate Group, University of California, Merced, Merced, CA 95343, USA
2
Oceanographic Research Institute, Autonomous University of Baja California, Ensenada 22860, Baja California, Mexico
*
Author to whom correspondence should be addressed.
Water 2024, 16(19), 2817; https://doi.org/10.3390/w16192817
Submission received: 31 August 2024 / Revised: 27 September 2024 / Accepted: 30 September 2024 / Published: 4 October 2024
(This article belongs to the Special Issue Safe Application of Reclaimed Water in Agriculture)
Versions Notes

Abstract

:
Here we report on preliminary efforts to assess the potential to use reclaimed water from municipal wastewater treatment plants for irrigation of vineyards in Napa Valley, California, USA and Valle de Guadalupe, Baja California, Mexico. Vineyards in Napa Valley use a range of source waters including 70 L/s of reclaimed water during the summertime irrigation season. Reclaimed water is secondary effluent that undergoes filtration and disinfection and meets stringent total coliform (<240 MPN/100 mL) and turbidity (10 NTU) requirements. Vineyards in Valle de Guadalupe currently use regional groundwater supplies of marginal quality, and there is interest in expanding source waters to include reclaimed water from nearby Ensenada or the more remote Tijuana. Valle de Guadalupe is drier than Napa Valley and has ongoing salinity management challenges, making the region more sensitive to using reclaimed water for irrigation. Several social and economic factors facilitated the implementation of reclaimed water reuse in Napa Valley for vineyard irrigation, including (1) formation of an assessment district by interested growers to help finance pipeline construction, (2) a long-term reclaimed water vineyard irrigation study by agricultural experts that confirmed the reclaimed water was safe, and (3) a well-defined and relatively low unit cost of reclaimed water. In Valle de Guadalupe, the federal government has approved a project to transport 1000 L/s of reclaimed water over 100 km from Tijuana to Valle de Guadalupe. Questions remain including financing of the project, reclaimed water quality, grower interest in using reclaimed water, and community concerns for such a large-scale program. In considering reclaimed water reuse in vineyards, a key issue is implementation of long-term studies showing that reclaimed water is effectively treated and is safe for irrigation, especially from the standpoint of salt content. In addition, the cost of reclaimed water needs to be comparable with traditional water sources. Finally, in addition to assessing economic constraints, social constraints and water user concerns should be comprehensively addressed in the context of a regional integrated water management framework.

1. Introduction

A unique challenge facing water managers in both California and Baja California is a critical need to diversify water supply sources for agriculture by adding treated effluent (reclaimed water) from municipal wastewater treatment plants (WWTPs) to the existing sources portfolio [1,2]. This region’s growing vineyard industry represents a unique and largely untapped demand that can be supplied with reclaimed water [3,4]. While studies have assessed the potential to reuse winery wastewater produced at California vineyards [5,6], there are no comprehensive comparative reviews regarding the use of reclaimed water in California and Baja California vineyards. The lack of studies can be due to the low number of vineyards currently using reclaimed water, which may be related to winemaker concerns surrounding the use of reclaimed water for crop irrigation [7,8]. But if carried out responsibly, the use of reclaimed water for vineyard irrigation can prove highly beneficial in providing vineyards with a secure and environmentally sustainable source of irrigation water in water-scarce regions [9]. Researchers at the University of California Merced are working with colleagues in Mexico to explore opportunities for collaboration on sustainable water resources management facilitated by a UC Alianza MX strategic grant on water resources management to increase climate extreme resilience in both Mexico and the United States.
In this communication, we discuss two vineyard municipal wastewater reuse case studies—one in Napa Valley, California, USA and one in Valle de Guadalupe, Baja California, Mexico. Both regions are known for growing premier wines, with the up-and-coming Valle de Guadalupe often referred to as the “Napa Valley of Mexico”. The regions differ in irrigation water sources and environmental, social, and economic constraints. Vineyards in Napa Valley, located north of San Francisco, California, rely on a mixture of potable, surface water, ground water, and precipitation, as well as highly treated reclaimed water from the Napa Sanitation District. Vineyards in Valle de Guadalupe, located in northwestern Baja California, rely on limited groundwater supplies, some with elevated salinity [10]. There is great interest in using reclaimed water in Valle de Guadalupe, either from nearby Ensenada or transported over 100 km from Tijuana. Valle de Guadalupe is much drier than Napa Valley. This makes the reuse of reclaimed water more of a challenge in Valle de Guadalupe since more irrigation is needed to ensure salts are flushed from the root zone. In both California and Mexico, clear criteria exist for the reuse of reclaimed water for irrigation with a focus on microbial contamination. As detailed in the communication, in Napa Valley, a “bottom up” approach to reclaimed water reuse for vineyard irrigation developed in which grape growers interested in irrigating with reclaimed water helped finance reclaimed water distribution infrastructure. Interest in using reclaimed water was facilitated by the high quality of the reclaimed water and a long-term irrigation study by agricultural experts financed by the Napa Sanitation District. In contrast, plans for reclaimed water reuse in Valle de Guadalupe are currently less transparent and may inspire less enthusiasm among potential users, who are unsure of reclaimed water quality, cost, and long-term impacts on vineyard production.

2. Case Study Backgrounds

2.1. Napa Valley, California, USA

Napa Valley is located 80 km north of San Francisco, California, USA and is considered one of the world’s finest wine-producing regions. The area attracts millions of visitors each year and produces around half of the state’s premium wines (above USD 15 per bottle). The Napa Sanitation District (NSD) provides wastewater services to around 83,000 residents and reclaimed water to a range of irrigation users including vineyards, golf courses, and commercial landscaping [11]. The NSD operates the Soscol WWTP with an average daily flow of 350 L/s (8 million gal/d). The plant provides preliminary treatment with screening and grit removal, primary treatment via settling, and secondary treatment with activated sludge and facultative pond system. At present, the Soscol WWTP has two seasonal modes of operation consisting of reclaimed water production and delivery in the irrigation season (April through October) and discharge to the Napa River in the winter.
The production of reclaimed water at the Soscol WWTP started in 1997. In addition to meeting stringent state effluent discharge requirements for treated wastewater, reclaimed water had to meet quality criteria established by the California State Water Resources Control Board as outlined in Title 22 of the California Code of Regulations [12]. For irrigation of food crops with potential to contact reclaimed water, the NSD is required to produce a “disinfected tertiary water type” that undergoes filtration and disinfection. Total coliform and turbidity levels must be below 240 MPN/100 mL and 10 NTU, respectively, in addition to other time-averaged criteria. Initially, reclaimed water was delivered to a handful of nearby landscape irrigators. In 2016, the NSD expanded the reclaimed water system, constructing 22.5 km of reclaimed water pipeline to serve a total irrigation area of 2930 ha (7250 acres) including 1650 ha (4070 acres) of vineyards.
Two key factors facilitated the implementation of this expansion. First, grape growers interested in irrigating with reclaimed water formed an assessment district that promoted interest in the use of reclaimed water and helped finance the pipeline construction. Second, to address grower concerns about the effects of vineyard irrigation with reclaimed water, the NSD funded a long-term irrigation study by agricultural experts at the University of California, Davis [13]. Key findings of the study included that reclaimed water quality was suitable for vineyard irrigation; that there was no long-term accumulation of salts and toxic ions in soils; and that, with proper nitrogen management, nutrients in reclaimed water can be beneficial to vineyards. The relatively wet winters in Napa, which has an annual rainfall of around 680 mm mostly between December and March, facilitate reclaimed water use in two ways (Mark Battany, personal correspondence). The higher rainfall means that the vineyards require modest levels of supplemental irrigation because the rainfall already provides for most of their water requirement. The high rainfall also ensures high rates of winter soil flushing so that salts do not accumulate in the rooting zone.
Reclaimed water production by the NSD has steadily increased, roughly doubling between 2015 and 2021 [11]. Currently, the NSD produces an estimated 3.95 million m3 of reclaimed water during the irrigation season, mostly for landscape irrigation. Around 40% of this reclaimed water is used by local vineyards. During the 2022 irrigation season, 1.4 million m3 (70 L/s) of reclaimed water was served to nearby vineyards [14]. Reclaimed water is rich in nutrients (7–15 mg N-NO3/L nitrate, 0.09–3.4 mg/L total phosphorus) and has a slightly elevated sodium absorption ratio (3.3–5.3 SU) (NSD, 2023); a value of 3.0 is generally considered suitable for unrestricted irrigation use [13].
Today, most of the effluent from the Soscol WWTP is being reclaimed during the irrigation season, so there are no plans to expand the current wastewater reclamation system. However, pumping facilities are being enhanced to ensure the reliability of reclaimed water delivery. An additional consideration related to the supply reliability of reclaimed water is droughts, which have resulted in a decrease in wastewater flows in California due to water conservation efforts [15]. Dry weather can also result in salinity increases in the NSD’s reclaimed water, as dry conditions promote saltwater intrusion from the nearby Napa River into shallow groundwater, which can infiltrate into older sewer systems. Drought-induced reduction in flow combined with salinity increases are being tracked by NSD managers, since they may impact the reclaimed water program in the future.

2.2. Valle De Guadalupe, Baja California, Mexico

The Mexican wine industry, while relatively small, is growing in economic importance. The industry generates approximately 7000 direct and 35,000 indirect jobs [16], and the market for domestic wine is valued at around MXN 4232 million (USD 248.9 million) per year [17]. A premier grape-growing region in Mexico is Valle de Guadalupe, located in northwestern Baja California. The valley’s aquifer provides water to 57% of the Mexican wine industry in a cultivated area of over 3000 ha [17] and promotes a thriving tourist economy.
Vineyards in Valle de Guadalupe rely on local groundwater and currently extract an estimated 25 million m3/year [18]. Since 2012, decreasing groundwater supply due to low rainfall has limited aquifer recharge, which, along with overallocation in groundwater extraction permits, has resulted in a cumulative groundwater overdraft of roughly 18 Mm3 and an average extraction-to-recharge ratio of about 1.3. The aquifer has an estimated total storage capacity of about 300 Mm3 [18]. Reclaimed water is an obvious option to consider and has been shown to be more cost-effective than building and operating a new branch to Ensenada from the Colorado River–Tijuana aqueduct [19]. In Mexico, the use of reclaimed water is regulated through the federal norm NOM-003-SEMARNAT-1997 [20], which is similar to California’s Title 22 regulations, with a focus on microbial contamination and traditional wastewater quality parameters including oil and grease, floating material, fecal coliform, and helminth eggs. Also, like California’s Title 22, the Mexican norm does not regulate important agriculture parameters such as total dissolved solids, nutrients, boron, or sodium adsorption ratio.
The geography of Valle de Guadalupe brings some key challenges for reclaimed water use compared with Napa. Annual rainfall in Valle de Guadalupe is around 350 mm, about half that of Napa. As a result, vineyards will need to apply much larger amounts of irrigation, and there will be less natural leaching of the soil profile with rainfall. If not managed properly, both factors can lead to accumulation of salts in the rooting zone to the detriment of the vines and wines. In addition, some wines produced in the Guadalupe Valley have relatively high salt content due to the vines being grown under salty conditions, which can affect wine flavor. As a result, some wine producers may be hesitant to use reclaimed water if its salinity is higher than current irrigation water supplies.
Two potential reclaimed water sources under consideration are nearby in Ensenada or further away in Tijuana. In Ensenada, the El Sauzal WWTP is the closest to Valle de Guadalupe. Total flow available during the irrigation season is around 89 L/s (2.0 million gal/d) and can meet around 11% of current groundwater extractions. Results from a 4-month monitoring period showed that the reclaimed water had a total dissolved solids (TDS) content of 934 mg/L, nitrate content of 0–18 mg-N/L, ammonia content of 0–10 mg-N/L, and phosphorus content of 2–20 mg-P/L; while the aquifer had 558 mg/L of TDS and 9–16 mg-N/L of nitrate, and ammonia and phosphate were undetected [20]. Several short-term studies have assessed the impact of irrigating grape vines with secondary effluent from the City of Ensenada WWTP [21,22]. Acosta-Zamorano et al. [23] carried out experiments with Tempranillo grapevines in Valle de Guadalupe and concluded that reclaimed water did not adversely affect the plant growth or basic parameters of ripe grapes (e.g., soluble solids, titratable acidity, pH, and nitrogen). Since the mineral content of reclaimed water was like groundwater used for irrigation, excessive mineral accumulation was not observed in grape must (freshly crushed fruit juice). In contrast, there is lack of information regarding Tijuana’s wastewater quality [24].
Another potential source of reclaimed water is from Tijuana. A project to convey reclaimed water from the City of Tijuana, located 113 km northwest, to Valle de Guadalupe has been approved by the federal government. However, to date, the project has been put on hold due to political, environmental, and economic concerns. The project would provide an estimated 1000 L/s, enough to irrigate all current vineyards and potentially allow the expansion of the irrigated area from the current ~3200 ha to ~6000 ha. The project would make Valle de Guadalupe the largest agricultural valley in the world to use reclaimed water for the irrigation of vineyards [25]. An institutional driver of water recycling in the region is the United States Environmental Protection Agency. The agency is working with CONAGUA, its peer regulatory institution in Mexico, to address pollution in the Tijuana River Valley and neighboring coastal areas [26]. The agency has committed USD 300 million to support infrastructure solutions to limit the discharge of untreated sewage to the Tijuana River, which flows from Tijuana through San Diego and discharges into the Pacific Ocean in the US. One of many potential strategies is to treat and recycle the water instead of discharging it to the Tijuana River. There is little irrigation demand for reclaimed water in the Tijuana region; thus, environmental managers are looking for surrounding areas where the reclaimed water can be reused. Nevertheless, the project has not taken off partly because farmers are concerned about increases in the price of the reclaimed water in Valle de Guadalupe, and there is still a lack of studies on the quality of Tijuana’s treated wastewater [24].

3. Key Issues of Wastewater Reuse for Vineyard Irrigation

3.1. Source Water Supply

Perhaps the most important issue related to the use of reclaimed water at vineyards is the characteristics of the water supply source (Table 1). After adequate primary (e.g., sedimentation) and secondary treatment (e.g., activated sludge) for organics removal, reclaimed water for irrigation needs to meet the state and federal criteria typically focusing on microbial contaminants to protect human health (e.g., fieldworkers and wine consumers). The location of the vineyard relative to the reclaimed water source is also of paramount importance, as water conveyance facilities are capital intensive (see Section 3.6).

3.2. Source Water Quality

In addition to the general water quality criteria noted above, vineyards have unique requirements that must be recognized in the context of wastewater use. In addition to microbial contamination, which is commonly the focus of reuse criteria, salinity is of major concern. Elevated salinity can compromise winegrape plant productivity, and the level of specific salts (e.g., chloride, sodium, and boron) is important, as they can be toxic or negatively affect soil quality [13]. Treated wastewater and reclaimed water can also be enriched with nitrogen and phosphorus, which can enhance grape plant growth as was seen in some case studies presented here [13,22]. But excess nitrogen may lead to excessive growth that diverts resources away from and shades grapes, thereby reducing fruit yields and lowering wine quality [13]. Trace metals and emerging contaminants, such as pharmaceuticals and personal care products (PPCPs) and per- and polyfluoroalkyl substances (PFAS), in treated wastewater may also be of concern, especially if they accumulate in plant tissue and affect grape or wine quality [9,27]. The use of reclaimed wastewater for irrigation can also lead to ongoing exposure of agricultural environments to antimicrobial-resistant microbes, antimicrobial drug residues, and antimicrobial resistance genes due primarily to the ecological pressure generated by antibiotics and other compounds found in wastewater [28,29]. Recent evidence suggests that antibiotics and antibiotic resistance genes can spread in agricultural soils, impacting soil microbiota and ecosystem health [30], especially in areas that lack advanced wastewater treatment technologies. Nevertheless, the application of treated wastewater for irrigation does not appear to significantly impact antibiotic-resistant levels in soil microbiome [29].

3.3. Polishing Treatment

Rather than solely relying on the WWTP to provide suitable water quality, on-site polishing treatment approaches can be used to promote wastewater reuse. If reclaimed water quality is high, on-site tertiary treatment can be implemented consisting of filtration and disinfection [31]. Constructed treatment wetlands and ponds are also effective at polishing secondary effluent, including removing nutrients, especially nitrate [32,33], and potentially transforming emerging contaminants of concern [34]. Managed aquifer storage can include the infiltration of reclaimed water into groundwater, potentially spread on flat vineyards during the winter. This strategy may have several advantages in the context of vineyard irrigation [35]. These include promoting water quality polishing via soil–water interactions during infiltration, recharging depleted aquifers during winter months when irrigation demand is low, and promoting water supply resilience in the face of increasing water insecurity. Constructed treatment wetlands and aquifer storage and recovery, which are surface-area intensive approaches, are potentially good fits with vineyard settings. However, if vineyards are to double as spreading areas, then more research is needed on the tolerance of vineyards to inundation. A survey of University of California Cooperative Extension Specialists estimated a tolerance to standing water of more than two weeks and less than one week before and after bud burst, respectively [36].

3.4. Long-Term Irrigation Studies

An important consideration for addressing winegrape grower concerns related to reclaimed water use is performing irrigation studies. The irrigation study for the Napa Valley case study is a good example [13]. The study was performed by independent agricultural researchers with the University of California, Davis. It included water quality assessment of reclaimed water and five other regional water sources, including well water, surface water, and domestic water, for a range of constituents (pH, salinity, alkalinity, and specific ions) on multiple sampling events. What makes such a study unique is that it tested soil quality from a vineyard that had been drip-irrigated for eight seasons with reclaimed water. Samples were collected at ten sites and two depths at the end of the irrigation season and tested for electrical conductivity, pH, and key ions. Calculations were then performed that showed no long-term salt buildup in soils and negligible impact of soil salinity on grape yields. As discussed above, several short-term irrigation studies have been performed on secondary effluent from the Ensenada WWTP, which can be a source of reclaimed water for Valle de Guadalupe [21,22]. These studies focused on grape and grapevine growth and quality, an aspect that was not assessed in the Napa Valley irrigation study. A recent irrigation study in the French Languedoc region tested four different water types (potable water, surface water, and two classes of reclaimed water) on vineyard plots over three years [31].

3.5. Social Constraints

A key social constraint is grape grower, wine consumer, and community acceptance of reclaimed water use for vineyard irrigation. While many studies have been performed on public perception of reclaimed water use in general, few have been performed on grower attitudes toward use of reclaimed water for agricultural irrigation. A recent survey of growers in the US Southwest found that around half rated “non-traditional sources” of water as important, but they were more inclined to use this water on forage crops vs food crops [37]. The study showed that providing growers with information documenting non-traditional sources as safe enhanced acceptance, highlighting the importance of reclaimed water use studies and outreach prior to full-scale irrigation at vineyards [13,31]. Mendoza-Espinosa et al. [8] conducted a survey of wine consumers and winemakers in Valle de Guadalupe to assess acceptance of reclaimed water for irrigation. Around 80% of the public were in favor of consuming wine produced via reclaimed water assuming its quality was safe to use for irrigation. Around 80% of grape growers and winemakers recognized the potential of using reclaimed water for vineyard irrigation but called for adequate operation of WWTPs and proper supervision of reclaimed water quality by a trustworthy third party. The rest did not favor reclaimed water use due to possible high cost of water and potential rejection by wine consumers, especially outside Mexico.
Another consideration is acceptance by the broader community of using reclaimed water to expand water availability, which can have several impacts including expanded agricultural and urban development. A recent newspaper article highlights the social and land use changes that have unfolded in Valle de Guadalupe as tourism and development has ballooned [38]. Without thoughtful planning, these changes can be exacerbated with a new, plentiful water supply. With the complexity of these projects, they should be implemented in the context of a regional integrated water management framework, which aims to coordinate development and management of water resources to optimize economic and social welfare in an equitable and environmentally sustainable manner [1,25,39,40]. In addition, life cycle assessment [41] and multi-criteria methodological approaches [42] can be used to comprehensively assess the economic, environmental, and societal aspects of reclaimed water use for vineyard irrigation.
An additional common theme in the implementation of vineyard irrigation with reclaimed water was the need for an organization to interface between the reclaimed water producer and users to facilitate project implementation and/or operation. This is a recognized challenge in many reclaimed water reuse projects [43]. In the case of Napa Valley, this consisted of an assessment district made up of vineyards interested in using reclaimed water that helped finance pipeline construction. For the reclaimed water irrigation project in the Languedoc region of France, an irrigators association was created to manage the distribution of reclaimed water to vineyards [31]. In Valle de Guadalupe, such an organization is yet to be considered.

3.6. Economic Constraints

Costs associated with wastewater treatment and water conveyance infrastructure are the primary economic barriers to reuse of reclaimed water for irrigation [11,44,45]. Wastewater treatment is chemical and energy intensive, making it an inherently expensive endeavor. As reclaimed water cannot be distributed in existing potable water conveyance systems, costly new distribution systems are commonly needed. Making the cost of reclaimed water competitive with the cost of traditional water sources is critical for project implementation. In many cases, the cost of reclaimed water is competitive with the development of alternative sources such as desalination or long-range transport [9]. Government grants or subsidies can facilitate implementation of reclaimed water reuse by lowering costs for end users [43]. Subsidies can support a range of actions such as planning, technical assistance, pilot studies, and construction. Other creative subsidies to support reclaimed water reuse include targeted tax breaks and credits for pollution abatement [43]. The cost of reclaimed water can be partially mitigated in the context of vineyard irrigation [11]. For example, the use of reclaimed water relatively rich in minerals and nutrients can improve soil health and promote plant growth, lowering soil treatment and fertilizer costs. In addition, there is an intrinsic value to having a nearly constant supply of urban wastewater available during periods of limited existing water supply. The use of managed aquifer recharge, in which reclaimed water is infiltrated into regional groundwater, can alleviate the need for costly transmission systems such as pipelines or canals. Moreover, it avoids potential sanitary, psychological, and aesthetic problems associated with direct use via pipelines and storage in surface reservoirs [46].
In the Napa Valley case study, the wastewater district did not expand its reclaimed water distribution system until regional stakeholders were willing to help finance construction. The 2016 pipeline expansion, financed in part by reclaimed water users, cost around USD 29.5 million (2016 USD). In 2022, reclaimed water served to vineyards cost 0.54 USD/m3 (USD 2.05 per 1000 gal) [14]. These costs are competitive with the regional cost of potable water for irrigation (~USD 7–11 per 1000 gal) and, as noted in [11], can be lower than the cost of developing new alternative sources of water. In the case of the project to transport wastewater from Tijuana to Valle de Guadalupe, construction and operation costs are high. Construction costs are estimated at MXN 4137 million (USD 243 million) and annual operating costs at MXN 82.7 million (USD 4.8 million) [24]. Although the proposed unit cost of water to irrigators in 2016 was MXN 13 per cubic meter (0.72 USD/m3), the cost increased to MXN 20 per cubic meter (1.11 USD/m3) by 2019 [25]. But the actual cost of reclaimed water is currently in contention by the farmers, as the water authorities have yet to detail how the water will be treated and transported to the valley.

4. Conclusions

Reclaimed water reuse for vineyard irrigation has proven safe and effective in Napa Valley, California and some other sites around the world. The approach also holds promise for water-limited Valle de Guadalupe, Baja California. While focusing on the California and Baja California region, this communication is relevant for wine-producing regions throughout the world that currently face water scarcity challenges. Key benefits of reclaimed water reuse for vineyard irrigation include diversification of water sources in a time of growing water insecurity, especially in arid and semi-arid climates, and enhanced plant growth resulting from nutrients in reclaimed water. Key challenges include high costs associated with wastewater treatment and reclaimed water distribution, concerns related to water quality, particularly salinity and emerging contaminants, and the need for a regional integrated water management approach that takes both social and economic constraints into account. Managed aquifer recharge is an exciting approach that can facilitate reuse of reclaimed water for vineyard irrigation by promoting water treatment during infiltration while simplifying water distribution to users via existing wells.
Based on this work and ongoing interviews with regional stakeholder in both California and Baja California, the team will assess the potential for managed aquifer recharge of the Valle de Guadalupe groundwater basin with reclaimed water from the Ensenada region. This study will focus on not only water quantity but also water quality, particularly salinity and bacterial and organic constituents, to ensure that enhanced water supplies are appropriate for vineyard irrigation. We also plan to continue to evaluate local stakeholder attitudes to the use of reclaimed water for vineyard irrigation in Valle de Guadalupe.

Author Contributions

M.B., L.M.-E., J.A.M. and C.M. conceptualized the paper. M.B. and L.M.-E. led the design and drafting of the manuscript with input and review from J.A.M., C.M., T.C.H. and J.M.-A. All authors contributed to the article and approved the submitted version. All authors have read and agreed to the published version of the manuscript.

Funding

This communication was facilitated by the UC ALIANZA MX strategic grant IRGUCMX2021-02 Water Management to Increase Climate Extreme Resilience for Agriculture, Ecosystems and Communities in the US and Mexico.

Data Availability Statement

Data are available from the authors or from the references cited. Contact the lead author for any data needs related to this communication.

Acknowledgments

The authors would like to thank Andrew Damron, Assistant General Manager of Napa Sanitation District, for sharing information regarding his district’s reclaimed water operations; Mark Battany, University of California Cooperative Extension Water Management and Biometeorology Advisor, for his review of our draft manuscript; and Astrid Hernández from Autonomous University of Baja California, Ensenada for providing the Tijuana and Valle de Guadalupe map. We also thank the anonymous reviewers of the manuscript for their input. The views expressed herein are solely those of the authors and do not represent the official policies or positions of any supporting or noted agencies.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that can be construed as a potential conflict of interest.

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Table 1. Summary of Key Issues of Wastewater Reuse for Vineyard Irrigation.
Table 1. Summary of Key Issues of Wastewater Reuse for Vineyard Irrigation.
Source Water Supply
Treatment levelTreatment of wastewater for removal of organics and disinfection required
LocationProximity of wastewater treatment plant to vineyard
Water qualitySalinity levels and seasonality of salinity
Supply alternativeReclaimed water vs surface water vs groundwater; different levels of nutrient ratios and salinity
Polishing Treatment
Filtration Filtration and disinfection of treated wastewater before irrigation
Natural treatment systemsUse of constructed treatment wetlands for excess nitrogen removal and transformation of emerging contaminants
Source Water Quality
Microbiological contaminantsModerately low levels of microbial contaminants acceptable for use of reclaimed water for vineyard irrigation; Mexico crop irrigation criteria: fecal coliform below 1000 MPN/100 mL; California Title 22 criteria: total coliform below 240 MPN/100 mL
Chloride toxicityDepends on irrigation method, leaching fraction, and plant varieties; typically want chloride < 250–1000 mg/L for drip irrigation
Boron toxicityGrapes are particularly sensitive to boron; guidelines for boron tolerance are limited, but general boron target is <1 mg/L
Sodium toxicityExcessive sodium leads to nutritional imbalances and poor soil quality; presence of calcium and magnesium mitigates negative impacts
Excess nitrogenWhile some nitrogen can enhance growth, too much can lead to vigorous vine growth, reduced fruit yield, and increased risk of vine disease
Heavy metalsSome sensitivity to heavy metals including arsenic, cadmium, chromium, copper, molybdenum, and selenium
Emerging contaminantsGrowing concern related to plant tissue uptake of some persistent organic contaminants, such as polyfluoroalkyl substances or “PFAS”
Long-Term Irrigation Studies
Soil qualityFocus on root zone soil salinity and effects on grape yield, heavy metal levels in soil, and reclaimed water quality that can impede soil quality
Plant growthFocus on grape plant growth and yield
Grape and wine qualityFocus on total acidity, volatile acidity, and alcohol and sugar content of wine and grapes; assess presence and uptake of persistent organic contaminants
Ground water impactsAssess impacts of reclaimed water reuse on groundwater quality including microbial contaminants, salinity, and nitrate
Social Constraints
Social acceptancePublic in favor of using reclaimed water for wine production; grape growers will consider using reclaimed water if treated and distributed by trustworthy entity; small fraction of growers reject the idea
Irrigator associationAssociation of vineyard water users to advocate for reclaimed water use and purchase and distribute reclaimed water to wine growers
Economic Constraints
Water costCost of reclaimed water compared with traditional water supplies
Government financingSupport of economically important vineyards in water-limited regions by partly subsidizing upfront costs of reclaimed water systems
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Beutel, M.; Mendoza-Espinosa, L.; Medina, C.; Morandé, J.A.; Harmon, T.C.; Medellín-Azuara, J. Achieving Responsible Reclaimed Water Reuse for Vineyard Irrigation: Lessons from Napa Valley, California and Valle de Guadalupe, Baja California. Water 2024, 16, 2817. https://doi.org/10.3390/w16192817

AMA Style

Beutel M, Mendoza-Espinosa L, Medina C, Morandé JA, Harmon TC, Medellín-Azuara J. Achieving Responsible Reclaimed Water Reuse for Vineyard Irrigation: Lessons from Napa Valley, California and Valle de Guadalupe, Baja California. Water. 2024; 16(19):2817. https://doi.org/10.3390/w16192817

Chicago/Turabian Style

Beutel, Marc, Leopoldo Mendoza-Espinosa, Clara Medina, Jorge Andrés Morandé, Thomas C. Harmon, and Josué Medellín-Azuara. 2024. "Achieving Responsible Reclaimed Water Reuse for Vineyard Irrigation: Lessons from Napa Valley, California and Valle de Guadalupe, Baja California" Water 16, no. 19: 2817. https://doi.org/10.3390/w16192817

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