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Review

Nitrate and Bacterial Loads in Dairy Cattle Drinking Water and Potential Treatment Options for Pollutants—A Review

by
Ceilidh Douglas
1,2 and
Pramod Pandey
1,2,*
1
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
2
Biological and Agricultural Engineering Department, University of California, Davis, CA 95616, USA
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(6), 3017; https://doi.org/10.3390/app15063017
Submission received: 14 January 2025 / Revised: 3 March 2025 / Accepted: 5 March 2025 / Published: 11 March 2025
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Abstract

:
The impacts of dairy farm manure production on the environment and surrounding ecosystems in terms of greenhouse gas emissions and eutrophication are frequently studied and discussed, but the implications for the dairy cattle themselves that drink water predominantly sourced from surrounding groundwater commonly polluted with nitrates and bacteria from manure and surrounding crop fertilization applications are not often prioritized. This study reviews and synthesizes relevant literature connecting groundwater pollution—in terms of nitrates and bacteria—as it relates to water quality for dairy cattle consumption and the health and milk production implications and outlines pre-existing treatment and prevention options for nitrates and bacteria in conventional applications as well and the status of treatment options for dairy cattle drinking water specifically. After evaluating potential treatment options, point-of-use filtration is identified as a possible low-cost and customizable treatment option for treating dairy cattle drinking water with advantages, potential disadvantages, and filtration media options discussed. Additionally, the need for further research and testing to determine the capacity in field-scale applications is identified.

1. Introduction

Dairy farms, with individual lactating cows producing an average of 45–55 kg of manure per day, output high amounts of manure typically applied to surrounding land [1]. This can be an acute source of nitrate and bacterial loads, which is a concern in terms of environmental impacts (i.e., eutrophication, greenhouse gas (GHG) emissions) but can also be a concern for the health of the cattle themselves [2]. In combination with high nitrate loads from surrounding croplands via synthetic fertilizers, nitrate and bacteria from manure can seep into groundwater, which is the main drinking water source for dairy cattle, collected via wells and dispensed in troughs.
There is a lack of regulatory guidelines surrounding acceptable levels of nitrate and bacteria in dairy cattle drinking water (except for grade A dairies, which regulate that fecal coliform remain below zero in cattle drinking water) [3,4]. In general, USDA grade standards for dairies are optional, and it indicates that the milk production and processing is performed under stringent sanitation standards. Studies have shown that high levels of nitrate can lead to troubled breathing, infertility issues, and decreased milk production in cattle, and bacterial contamination can lead to diseases such as leptospirosis and brucellosis [5,6,7]. In addition to negatively impacting cattle health, decreased water quality can also indirectly reduce milk production by causing cattle to drink less water, which is a large factor in milk production volume [8].
In addition to a lack of contaminant regulations and widespread monitoring, there is a shortage of point-of-use treatment options available for reducing nitrate and bacteria levels in trough water. In general, a point-of-use water treatment system offers the water treatment at a specific location, where the water is being used. As an example, a point-of-use system for a faucet will treat only the water drawn from the faucet rather than the entire water supply. Often, point-of-use water treatment systems based on the reverse osmosis (RO) process are used to treat water at a single fixture/point. Treatment options such as UV light, raking/dredging, and fish are algaecides known to control algae growth in drinking water; however, these systems are yet to be tested for livestock drinking water. Some of the treatment and prevention techniques for bacteria include the use of chemical disinfectants and frequent trough cleaning [9]. For nitrate, there are even fewer treatment options, with the primary recommendation to direct cattle to an alternative water source, which is not usually feasible for groundwater-sourced drinking water [10]. Long-term prevention options for nitrate exist in the form of manure management strategies, which decrease nitrate loads into groundwater, but with the trend of increasing farm size and nitrates persisting in groundwater for up to decades, there still exists a need for point-of-use treatment [11]. Traditional options such as slow sand filtration (SSF), constructed wetlands (CW), and artificial groundwater recharge (AGR) are used for controlling the transport of contaminants into water bodies. As an example, SSF uses a sand bed to remove pathogenic bacteria, turbidity, and suspended particles. SSF is considered to be a cost-effective option for controlling the pollution in drinking water. In constructed wetland systems, wastewater is treated by wetland plants, microbes, and soil filters. In addition, AGR systems are based on spreading water on the larger land area for improving infiltration into the soil, which assists in restoring groundwater and controlling the contaminant transport into groundwater. While these are effective options, the scale is an issue for many locations. For example, these systems require a larger area and an extended period of time for treating the water, and it could be challenging to implement these treatment systems in dairy farms.
The objective of this paper is to perform a review of relevant literature, providing an overview of the sources, recommended levels, and pre-existing treatment options for both nitrate and bacteria in dairy cattle drinking water explored in further detail. This paper identifies the need for point-of-use treatment options for nitrate and bacterial contamination in dairy cattle drinking water. Filtration is identified as a possible treatment option with a discussion of pros and cons and potential media selection as well as a discussion of relevant research gaps.

2. Materials and Methods

The methodology involved for compiling the literature review largely included the use of the Google Scholar database to gather information on contaminant prevalence studies, treatment mechanisms, and media options for both nitrate and bacterial groundwater pollution removal. Keywords utilized within these searches included “nitrate”, “bacteria”, “groundwater”, “dairy cattle drinking water quality”, and “treatment”. Different Centers for Disease Control and Prevention (CDC), U.S. Environmental Protection Agency (U.S. EPA), U.S. Food and Drug Administration (U.S. FDA), and university extension webpages were utilized to gather information about relevant regulations, health impacts, and water quality needs for dairy cattle specifically as well as pre-existing conventional and dairy-farm specific treatment options. Studies from the previous decade were prioritized, but because there is a limited number of published works about the health implications of different contaminants for cattle, older frequently cited published works were referenced because the pollutant level recommendations for dairy cattle are assumed to be relatively stable metrics.
Relevant key information was compiled and organized into different sections relevant to this paper, such as pollutants of concern for dairy cattle drinking water, prevalence and source of nitrate and bacteria in groundwater, recommended guidelines for each contaminant and monitored levels, and pre-existing treatment options for both nitrate and bacteria removal, and—once adsorption was identified as one of the most promising options—studies exploring nitrate and bacteria removal via adsorption were compiled to delineate possible advantages and disadvantages of the treatment mechanism as well as different filtration media.
The purpose of this review is to create a comprehensive understanding of the factors impacting dairy cattle drinking water quality, their importance, and possible solutions for high levels of nitrate and bacterial pollution for the specific application of dairy cattle trough drinking water.

3. Nitrate and Bacterial Contamination in Dairy Cattle Drinking Water

3.1. Nitrate and Microbial Pollution Present in Dairy Cattle Drinking Water: Sources, Recommended Levels, and Health Impacts

Manure produced on dairy farms is considered to be a large source of GHG emissions such as methane and nitrous oxide, but also, importantly, excessive amounts can be an acute source of certain pollutants such as nitrate and can contribute to elevated nutrient and bacterial loads in groundwater and surrounding surface water [2]. This can be detrimental to surrounding ecosystems as well as the people and animals relying on local water sources for drinking water. Dairy cattle predominantly drink water from troughs (as seen in Figure 1), and this water is often sourced from groundwater and is rarely treated before consumption.
Two major pollutants in water that may pose risks to cattle are nitrate and E. coli. Elevated levels of nitrate in groundwater are often linked with the storage, handling, and disposal of livestock manure and agriculture more broadly (i.e., synthetic fertilizer inputs). Similarly, microbial pollutants such as elevated levels of E. coli in water are caused by manure, and many outbreaks are linked with manure-borne pathogens. When manure is flushed or washed away as runoff, it can contribute to elevated levels of nitrate in surface water, and because of nitrate’s high solubility, it can easily seep into groundwater [12]. The maximum contaminant level (MCL) of nitrate in human drinking water, set by the EPA, is 10 mg/L of NO3−–N (as nitrogen) and 44 mg/L NO3− (as nitrate) because it can lead to harmful health effects such as methemoglobinemia, or blue-baby syndrome, which causes a baby’s skin to turn blue as well as being linked to cancer and other health effects [13,14].
Even though there are no regulatory standards for livestock drinking water, it is recommended that nitrate levels for cattle/livestock drinking water stay below 100 ppm. The U.S. EPA’s standard for a safe level of nitrate (≈10 ppm) in drinking water for humans is considered to be safe for livestock also [15]. This is largely because—similar to humans—nitrate can reduce to nitrite in the cow’s system, which decreases the blood’s ability to transport oxygen [16]. Acute nitrate concentrations have dangerous consequences for cattle health (in some cases even leading to death), but long-term chronic toxicity is a more common issue [5,6].
Calves and lactating cows are especially susceptible to high levels of nitrate. It has been shown to decrease their water consumption and, in turn, negatively impact their milk supply in addition to negatively affecting fertility [8]. The risk from nitrate ingestion is additive, so limiting nitrate in drinking water is especially important when high levels of nitrate are present in feed. High levels in feed may be due to several factors such as the type of crop species having higher nitrate accumulation potential (i.e., sorghum), high rates of nitrate application in the form of fertilizers, and conditions of limited plant growth such as droughts [15,16]. Both nitrate and phosphate—which is also found in manure—can lead to eutrophication in surface waters, which is the excessive growth of algae and the subsequent decrease in dissolved oxygen, which is harmful for aquatic ecosystems [17].
High levels of nitrate in groundwater are not only an issue when directly consumed, but nitrate and phosphate can also contribute to algae growth in trough waters, especially in sunny and warm conditions (Figure 1). The presence of algae can negatively affect the odor and taste of the water, which is known to decrease the amount of water consumed by cattle and can decrease the amount of milk produced [18]. Some forms of algae (blue-green algae) can even be toxic for cattle and can lead to much more serious health effects such as “muscle tremors, diarrhea, labored breathing, lack of coordination, liver damage and death” [8].
Some measures can be taken to reduce the risk of algae growing in troughs but can be labor intensive or require frequent monitoring. These include the addition of chemicals such as bleach or copper sulfate (which must be carefully dosed to avoid causing other health issues for cattle), moving troughs to shaded areas, regular scrubbing and cleaning, and even the addition of goldfish, which can introduce other upkeeping needs [19]. Point-of-use filtration treatment could provide a treatment method that, by reducing the amount of nitrate, prevents the growth of some of these harmful algae.
Often rural drinking water systems are highly susceptible to bacterial pollution from livestock manure (in addition to domestic wastewater sources), and most human waterborne diseases occur due to contamination in these systems [20]. Groundwater sources for drinking water need to be monitored for bacteria because of their prevalence and ability to cause diseases in both humans and animals [7]. It is suggested that total and fecal coliform counts should remain below 1 per 100 mL for calves and 15 and 10 per 100 mL, respectively, for adult cattle [16]. The only federal regulations to exist for the bacteriological quality of animal drinking water, however, exist for animals producing grade A milk products, where water must have no detectable fecal coliform [4].
Highly concentrated livestock operations, classified by the EPA as concentrated animal feeding operations (CAFOs), are regulated as point sources of pollution under the National Pollutant Discharge Elimination System (NPDES). Through this system, individual permits aim to control discharge levels of contaminants such as nitrogen, phosphorus, and bacteria as well as biological oxygen demand (BOD) and total dissolved solids [21]. Livestock operations at smaller scales are often not regulated at the same levels but can still contribute high levels of pollution. Additionally, private wells in rural areas are much less likely to be monitored and regulated (currently not federally regulated and seldom regulated at the state level) [22]. In general, rural communities typically have fewer resources available for treating potentially polluted water [2,23]. Low-cost water treatment options, therefore, could be a valuable option for improving livestock drinking water quality and could potentially even be adapted to treat water to levels acceptable for human consumption. Many existing low-cost water treatment options such as boiling water, ceramic filters, fabric filtration, chlorination, and UV disinfection are reported to be effective systems; however, these are rarely used for treating animal drinking water.

3.2. Current Manure Handling Practices

Throughout the United States, rural farm operations typically handle manure by flushing water into lagoons intended to pretreat and settle out solids. Alternatively, solids can be separated mechanically. After recycling the liquids for flushing, they are then applied to nearby fields for irrigation [24]. The solid manure is commonly applied to nearby lands but can also be further treated for other uses such as composting, anaerobic digestion, or cattle bedding [25,26]. Liquids have a higher proportion of nitrate (as compared to the solids) and have high variability in concentration but have been measured to range from around 100 mg/L to 1170 mg/L [27]. Dairy farm manure loads from land application, lagoon leaching, corrals, etc., can lead to elevated groundwater nitrate concentrations. A study surveying nitrate concentrations surrounding dairy farms throughout California’s San Joaquin Valley found that nitrate-N concentrations in shallow wells were 64 mg/L (around 283 mg/L nitrate) as compared to 24 mg/L (106 mg/L nitrate) in shallow wells upgradient from the dairy farms and source of manure [28].
In addition to dairy farms themselves being large contributors to local groundwater nitrate concentrations, nearby croplands subject to synthetic fertilizer inputs are another risk factor of high nitrate concentrations in ground and surface waters. In fact, cropland contributes approximately 96% of leached nitrate present in groundwater basins [29].
Studies have also shown that livestock wastewater can contribute to elevated indicator bacteria concentrations in groundwater (i.e., two to three orders of magnitude higher than background bacteria levels). This is especially true following rainfall events, which can increase the infiltration of bacteria from soil retention to groundwater [30]. Another study conducted in Argentina sampled groundwater surrounding dairy farms and found levels of total coliform between 0 and 1600 most probable number (MPN)/100 mL and levels of fecal coliform between 0 and 140 MPN/100 mL. While the upper limits of those measured ranges are above recommended levels for cattle, about 50% of the samples, however, were determined to be suitable for human consumption with concentrations close to 0 MPN/100 mL [31]. These results are consistent with observations in the literature that while dairy farms contribute bacteria to groundwater and consequently trough water, a major source of bacterial pollution in cattle drinking water troughs could be from the cows themselves via cud, dust, manure, etc. [9]. Figure 2 outlines major pathways for nitrate and bacterial inputs to reach dairy cattle drinking water and some of the short-term and acute impacts as well as longer-term or indirect impacts.

3.3. Water Treatment Options

Many treatment methods are available for the removal of nitrate and bacterial contamination for drinking water applications, all with their benefits and drawbacks, making some methods better suited for different applications than others. Lactating dairy cattle have high water consumption rates, requiring an average of 45 to 128 L—even up to 189 L of water per day, depending on multiple factors such as ambient temperature, water content in feed, and milk production [32]. Troughs usually service approximately 20 cattle, so a trough should supply roughly 2649 L to 3785 L per day [33]. Point-of-use treatment methods for dairy cattle drinking water, therefore, would have to be adaptable for high flow rates in addition to being low-cost and low-maintenance to increase appeal for farmers.
Some of the most common treatment methods for removing nitrate ions from water include distillation, ion exchange, RO, and electrodialysis. Distillation is the energy-intensive process of evaporating water and collecting the condensed water that is free of many contaminants including nitrate, bacteria, and some viruses as well [34]. While it produces high-quality water and is available for point-of-use systems, it is expensive and slow. Ion exchange is another treatment option for the removal of nitrate and other unwanted ions, and it can be scaled up or down for different capacity levels. Some of the drawbacks of this method, however, are that it requires the disposal of wasted brine solution, is subject to reduced removal efficiency with the presence of competing ions, requires chemical additions, and is not effective at removing bacteria [35]. The RO process uses pressure to force water through a semipermeable membrane and can remove both nitrate and bacteria (and many other contaminants) in both large- and small-scale applications, but it is usually energy intensive and expensive [36,37].
In addition to the aforementioned physical removal methods, biological denitrification provides another treatment method. It is currently a less feasible option for treating water for several reasons including high maintenance requirements due to the addition of substrates and nutrients. Additionally, it is not a well-established treatment method, and it does not provide a method for bacterial removal, so it would need to be combined with another treatment method for animal drinking water applications.
Similar to biological denitrification, chemical denitrification offers a treatment mechanism that does not physically remove nitrate into a separate waste stream and instead relies on reducing nitrate to less harmful forms, such as nitrogen gas. The chemical treatment method, however, has not been developed at full scale, depends on pH adjustments, and does not remove bacterial pollutants [2].
For dairy cattle drinking water sources with high nitrate concentrations, the most common recommendation is to change the water source or dilute the water with cleaner sources because options like distillation and RO may be too expensive [10]. While this may be feasible for cows drinking from surface waters, drinking water sourced from groundwater might not be easily changed or supplemented.
Within large-scale water treatment plants, bacterial contamination is usually treated with the addition of chemical disinfectants such as chlorine but can also be treated using ozonation or ultraviolet (UV) disinfection [38]. Some of these same treatment options are available for treating individual drinking water troughs. It is recommended that farmers clean troughs regularly as infrequent cleaning allows bacteria to breed, but disinfectant chemicals can also be added [9]. Some of the suggested disinfectants include bleach, sodium dichloroisocyanurate, calcium hypochlorite, and chlorine dioxide, and it is recommended to disinfect troughs at least twice a year. A drawback of this treatment method is the need to carefully dose the bleach because too high of a concentration may bring the chlorine to unhealthy levels and deter cattle from drinking [18]. Distillation and RO are available treatment options but not readily relied upon in the context of trough water treatment because of their high energy requirements and other downsides previously mentioned as well as UV’s decreased efficiency for waters with high levels of suspended solids [39].
Compared to filtration, adsorption offers an option for water treatment that is low-cost, relatively easy to maintain, has a high removal efficiency, and is able to remove many different contaminants [40]. In a filtration system, a porous medium (such as sand, activated carbon, and fabrics) is used to form a barrier to physically trap the contaminants. However, in the adsorption system, media such as carbon filters, zeolites, and silica gel are used, which bind the contaminants to the media surface. In an adsorption process, contaminants, such as ions, are removed through attaching ions to the surface of a medium (via physical or chemical sorption) [12,41,42]. Adsorption is usually facilitated through either filtration, such as column-based filtration where a solution is run through a column filled with media, or batch adsorption where the contaminated solution is mixed in a closed system with the adsorbent media for a given amount of time [43]. Different media can be utilized for the targeted adsorption of particular contaminants, but filtration is generally used to remove contaminants such as organic materials, suspended solids, and microorganisms in conventional water treatment systems [44].
One of the downsides of filtration is its reduced efficiency over time, necessitating regeneration, backwashing, or media replacement. Filtration has not been commonly used as a nitrate removal treatment option in large-scale treatment facilities; in fact, it is not listed as one of the best available technologies (BAT) by the California Code of Regulations (ion exchange, RO, and electrodialysis are considered to be BAT) [12,41,42]. Regardless, many studies have evaluated the effectiveness of nitrate removal via adsorption [12,41,42]. For pilot-scale or individual point-of-use treatment systems, adsorption offers a treatment mechanism that may have higher economic feasibility than other treatment options better suited for centralized treatment because of its lower capital or energy costs.

3.4. Filter Media Options for Adsorption

Filtration media selection is important to optimize the targeted removal of both nitrate and bacteria, affecting the pollutant removal efficiency as well as the overall cost of the treatment system. Several materials have been optimized for nitrate or bacteria filtration via chemical or physical treatment (i.e., activated carbon modified with aluminum hydroxychloride for improved bacteria removal). Further, chemically activated biochar has been found to be suitable for nitrate adsorption [12,45]. While these materials are promising and may be more effective than natural materials, they are currently either not economically viable, commercially available, or both. High media costs—and thus overall treatment costs—may be a barrier for implementing water quality improvement measures. Choosing media for filtration that is commercially available, low cost, natural, and safe for cattle is important for improving the likelihood of farmers choosing filtration as a treatment option for improving the water quality for the health of their cattle.
Activated charcoal (AC) is a commonly used filter medium for a wide number of applications because of its high surface area, porosity, and large number of active sites. The granular (>0.2 mm particles) and powdered forms (<0.2 mm particles) are commonly used to filter out organics, heavy metals, and factors affecting taste and odor in wastewater but are not often used for nitrate removal in conventional water treatment facilities [46,47]. Raw activated carbon is initially negatively charged, which is not optimal for the adsorption of negatively charged nitrate ions or bacteria, but many different forms of physical or chemical activation and further modification methods have been explored at the lab scale for optimized nitrate and bacteria removal with AC-based adsorbents [36,45,48]. Commercially available forms are commonly activated with heat and steam or chemicals including zinc chloride, phosphoric acid, sodium hydroxide, and potassium hydroxide, which can still achieve acceptable levels of nitrate removal for animal drinking water applications [49].
For bacteria removal, activated charcoal has been studied and found to be effective, but long-term efficiency has been found to decrease, and in some instances, the AC can even become a source of bacterial contamination itself [45]. The removal efficiency for nitrate has also been shown to decrease over time, necessitating periodic replacement, as is true with most filter media [48]. Activated charcoal has been explored as a soil amendment, however, or even as an additive to bedding or liquid manure lagoons, which could provide a convenient means of disposal of the media after use [50].
Sand is another commonly used natural, cheap, and readily available filtration medium used for water treatment. In conventional water treatment plants, it is often used within a multi-media filtration system designed to filter out suspended solids and inorganics, and in lab-scale experiments, it has been used in conjunction with other media such as biochar to filter nitrate and reduce the need for backwashing [51,52,53]. Slow sand filters have been used to filter nitrates via biological denitrification. The low flow rate (0.18 L/min) allows for the growth of a biofilm capable of reducing nitrate as well as filtering out pathogens [54,55].
Bentonite clay is another medium that is commonly used for adsorption within the context of water treatment. Raw forms have not been found to have high nitrate adsorption rates specifically, but bentonite is commonly used to prevent nitrogen leaching from lagoons on dairy farms, and modified forms have been able to achieve nitrate adsorption. Some studies have also evaluated it for its ability to filter pathogen indicators such as E. coli [12,56,57,58,59]. Additionally, bentonite has also been used as a soil amendment to enhance soil water and carbon retention, so it could be disposed of and recirculated easily onsite at a dairy farm [57,58,59].
Wood chips and other wood-based media (i.e., sawdust) have been used for biological denitrifying filters as a carbon source for the denitrifying bacteria [60,61,62]. Some studies have found sawdust to be an effective material at treating groundwater in permeable reactive barriers (PRBs) for removing nitrates [63]. It has also been evaluated for its bacterial removal potential, and it has been shown to reduce E. coli and other bacteria in column-based experiments [64]. The material is cheap and using it as filter media could provide a use for wood products commonly viewed as waste products (i.e., sawdust at lumber mills) [65]. Table 1 organizes some of the studies reviewed that investigate each material for the application of reducing aqueous nitrate and bacterial contaminants.
There is a new emphasis on developing strategies for managing manure and other agricultural wastewater in order to decrease the load of nitrates and pathogens infiltrating into groundwater and affecting drinking water. Other pollutants such as excess levels of salts/ions in livestock drinking water, which causes animal health problems, are needed to control for maintaining animal health and productivity [72,73,74]. While it is important and impactful to develop long-term strategies for reducing nitrate concentrations present in animal—and human—drinking water in rural applications, point-of-use treatment is still a viable and important option for the health of dairy cattle, and feasible and cost-effective technologies for treating drinking water already polluted are yet to be discovered. Studies have found an existing trend of decreasing the number of farms but with higher cattle densities as well as a trend of increasing nitrate concentrations in groundwater [11]. This, paired with the fact that nutrients such as nitrate often remain in groundwater for decades after the initial contamination, as well as the observation that much of the trough bacteria levels come from the cattle themselves, means that point-of-use treatment offers the best opportunity for improving the water quality in dairy cattle drinking water troughs, and adsorption offers a cheap, customizable, and relatively low maintenance option [29,75]. More importantly, it is a scalable option, and it can be developed for a single trough as well as for an entire dairy farm with many troughs. Overall, this review attempted to provide existing information on livestock drinking water, which indicates that this field of research is not well explored, and additional research is needed. This is particularly important considering that livestock health has the potential to impact human health, and poor animal health directly impacts food security. In livestock operations, water troughs are used to provide drinking water to cattle; however, these water troughs are also a major source of exposure of cattle to pathogenic bacteria including foodborne pathogens, which affect livestock health negatively [76,77]. Long-term study showed that contaminated drinking water poses risks to livestock, and improved water quality and effective hygiene measures can prevent the transmission of pathogens and improve animal health [78,79]. Improved water quality enhances production efficiency due to better rumen stability and bacterial activity [79,80]. In general, groundwater is the main water source for trough water, and increased level of nitrate in groundwater has a potential to affect livestock health negatively. For example, as part of the U.S Geological Survey in 2018, the National Water Quality As-sessment estimated that approximately 21% of private wells in agricultural areas exceed-ed the nitrate MCL of 44 mg/L, a much higher frequency than wells in other areas [81], and reducing nitrate levels in livestock drinking water may require on-farm treatment system. The installation of a livestock drinking water treatment system in a farm will likely increase the operational cost; however, the improvement in cattle health and improved production can compensate for the cost of achieving these improvements.

4. Conclusions

Some of the risk factors associated with elevated nitrate levels in cattle trough water include water sourced from shallow wells, close proximity to synthetic fertilizer and inputs, and well location downgradient from manure inputs. Elevated nitrate levels in drinking water are especially a concern for cattle health if there are already high levels of nitrate in feed. Bacteria pollution can be harmful for cattle health as well, and some of the risk factors associated are infrequent trough cleaning, infrequent trough refills, and seasonality effects.
While there are some treatment options available for bacteria present in troughs in terms of chemical additives and frequent cleaning, readily available and low-cost treatment options for nitrate contaminants are unavailable, and options for bacteria treatment may be less than ideal. Centralized or conventional treatment options for both contaminants have various advantages and disadvantages. Point-of-use adsorption treatment could provide an avenue for reducing the contaminant load in dairy cattle drinking water. This option is comparably low cost and customizable for decentralized trough treatment as compared to higher-cost nitrate and bacterial conventional treatment options.
One important design step for the identified method of treatment is media selection for targeted adsorption of nitrate and bacteria. Natural materials such as activated charcoal may be a good option due to its high adsorption capacity for many different contaminants, commercial availability, and low cost even though it might have reduced long-term removal efficiency. Other materials with chemical modifications may be an alternative with even higher nitrate and bacteria adsorption capacity but may have the disadvantage of cost and lack of commercial availability.
More research is needed to test different media within field-scale applications and identify optimal designs for treating nitrate (largely sourced from groundwater) and bacteria (sourced from both groundwater and the cattle themselves). Additionally, experimentation is needed to assess the feasibility and practicality of the point-of-use adsorption treatment on-site at dairy farms. This includes the duration for which media achieve effective contaminant removal, the required frequency of new media additions, related maintenance needs, and disposal and recyclability options on-site. The development of a point-of-use treatment system would also benefit from the continued development of low-cost filtration media modification for improved removal efficiency.

Author Contributions

C.D. and P.P. contributed to this manuscript in terms of conceptualization, revision, and editing. The first draft was produced by C.D. Conceptualization was performed by P.P. Data collection and writing were conducted by C.D. Critical review was performed by P.P. While completing graduate study, C.D. worked under P.P.’s supervision to complete this review. All authors have read and agreed to the published version of the manuscript.

Funding

Authors thank the support from the School of Veterinary Medicine and the University of California Agriculture and Natural Resources (UC ANR), University of California-Davis, Davis, CA, USA.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study.

Acknowledgments

Authors thank Noha Amaly, Prachi Pandey, Aditya Pandey, and Paola Duarte for facilitating discussion and critical thinking related to issues of animal drinking water.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 15 03017 g001
Figure 1. Typical setup of dairy cattle drinking water trough. Algae present indicates nitrate present, and certain forms may pose toxic threats to cattle.
Figure 1. Typical setup of dairy cattle drinking water trough. Algae present indicates nitrate present, and certain forms may pose toxic threats to cattle.
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Figure 2. Flowchart of major inputs of nitrate and bacteria in cattle drinking water on dairy farms and their acute and long-term impacts.
Figure 2. Flowchart of major inputs of nitrate and bacteria in cattle drinking water on dairy farms and their acute and long-term impacts.
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Table 1. Selected media and their assessed ability to remove nitrate and E. coli from aqueous solutions.
Table 1. Selected media and their assessed ability to remove nitrate and E. coli from aqueous solutions.
Media TypeTargeted Pollutant
(NO3− or E. coli)		Methods/ConditionsEffectivenessReference
Bentonite clayNO3−Varying percentages (0, 2, 4%) of bentonite added to sandy soils and leachate of fertilizer measured after filtering through columnsIncreasing amounts of bentonite decreased nitrate leaching and increased NO3− retention in soil (4% bentonite decreased leachate concentrations by 12–19%)[57,66]
NO3−Bentonite clay is modified with HDTMA and then mixed and centrifuged with nitrate solution (100 mg/L)The modification method modified the surface to be positive which greatly increased the nitrate adsorption of bentonite as compared to the unmodified form which was essentially ineffective[66,67,68]
NO3−Batch experimentation with unmodified bentonite and synthetic landfill leachate mixed together for varying durations and in different ambient temperatures with the mixture filtered and analyzed for nitrate (and other forms of N) concentrationsLonger mixing times and higher temperatures lead to higher adsorption rates. A maximum reduction of 17.33% nitrate was achieved with bentonite[67,69]
NO3−Bentonite clay activated with HCL used in batch experimentation with mixing and centrifugation to assess nitrate adsorptionThe activated bentonite is able to achieve an 80% nitrate ion reduction from aqueous solution with a maximum adsorption of 7.5 mg/g under ideal conditions[58,68,70]
Activated carbonNO3−GAC treated with both sodium hydroxide and a cationic surfactant used to assess nitrate adsorption within batch experimentsThe maximum adsorption capacity for the modified GAC found to be 21.51 mg/g [69]
NO3−A review of modified, composite, and raw forms of AC and its ability to adsorb nitrateModified and composite forms of AC generally have higher adsorption capacity for nitrate than raw forms[48,66,69]
E. coliPoint-of-use AC filtration units were installed at homes with private wells, and influent and effluent bacterial concentrations were counted and comparedAC filter effluent bacteria levels were elevated as compared to influent numbers but only if left stagnant overnight; with flushing (2 min), the AC filtered effluent had lower bacteria counts compared to influent[68,70,71]
E. coliCommercial activated carbon block filters were tested for their ability to filter E. coli under simulated household usage patterns for 29 daysAs compared to the spiked influent level, the effluent bacteria counts of E. coli varied from 24 to 60%[70,71]
E. coliAC modified with six different antimicrobial chemicals used for column filtration. Filter media post filtration are inoculated on agar plates, and colonies are counted after incubationAll six filter media showed >6 log removal, the recommended USEPA level for human drinking water, even with extended use[45]
Wood-based material (i.e., woodchips) NO3−Sawdust mixed into soil (30% by volume) and constructed into a denitrification wall to intercept groundwater with nitrate removal measured and calculatedOver the study duration of 1 year, it was determined that the denitrification wall can effectively reduce nitrate concentrations in groundwater[71]
NO3− and E. coliUpflow woodchip bioreactor columns designed to test the E. coli and nitrate removal capacity at different temperatures and hydraulic retention times At the higher ambient temperature (21.5 °C), the reactor achieved an 87% reduction and at 10 °C achieved a 75% reduction in E. coli levels compared to influent levels; the longer (24 h) HRT achieved a 96% reduction in nitrate[64]
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Douglas, C.; Pandey, P. Nitrate and Bacterial Loads in Dairy Cattle Drinking Water and Potential Treatment Options for Pollutants—A Review. Appl. Sci. 2025, 15, 3017. https://doi.org/10.3390/app15063017

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Douglas C, Pandey P. Nitrate and Bacterial Loads in Dairy Cattle Drinking Water and Potential Treatment Options for Pollutants—A Review. Applied Sciences. 2025; 15(6):3017. https://doi.org/10.3390/app15063017

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Douglas, Ceilidh, and Pramod Pandey. 2025. "Nitrate and Bacterial Loads in Dairy Cattle Drinking Water and Potential Treatment Options for Pollutants—A Review" Applied Sciences 15, no. 6: 3017. https://doi.org/10.3390/app15063017

APA Style

Douglas, C., & Pandey, P. (2025). Nitrate and Bacterial Loads in Dairy Cattle Drinking Water and Potential Treatment Options for Pollutants—A Review. Applied Sciences, 15(6), 3017. https://doi.org/10.3390/app15063017

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