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agriculture and drinking water quality for private wells

How Does Agriculture Pollute Private Wells?


Nearly 1.2 billion acres of the continental United States are used for agricultural practices. In addition to providing sustenance for millions, agriculture is an essential industry for many communities. But farming practices (particularly “factory farming”)—which include the use of pesticides and nitrate-rich fertilizers—have long been a source of contamination for drinking water supplies, especially for private well owners

If you live near agriculture, should you be worried about your drinking water? In this scenario guide, we’ll explore your potential contaminant risks, along with information on how to best test and treat your water.

    Table of Contents:

    Key Takeaways:

      • Runoff is the leading cause of agricultural pollution of drinking water supplies. Leading contaminants of concern from farming practices include:
        • Nitrates
        • Pesticides
        • Bacteria
        • Heavy metals
      • Testing your water is the best way to understand how your drinking water may be contaminated and by how much, as well as how to approach treatment 
      • Depending on your water’s specific contaminants, activated carbon filters, nanofiltration, and reverse osmosis can help treat water with agricultural contaminants

    How Does Living Near Agriculture Affect Well Water Quality?

    Agricultural drinking water contamination is largely the result of runoff. But the precise way your water is affected depends on a number of factors, including what type of farm it is and the kinds of pesticides (which include herbicides, insecticides, and fungicides) and fertilizers (including biosolids) used. The depth and age of your well, the region’s water table, subsoil, and bedrock all play a role as well.

    The primary contaminants of concern from farming practices include:

    • Nitrates
    • Bacteria
    • Heavy metals
    • Pesticides
    • Emerging contaminants (including PFAS and PPCPs) 
    how does living near agriculture affect your water

    What Is Agricultural Runoff? 

    Agricultural runoff is water from irrigation, rain, or snowmelt that does not soak into the soil but instead travels along its surface into streams and other water sources, collecting all sorts of contaminants in the process.

    Agricultural contaminants also leach or seep into the soil and penetrate down to groundwater sources, like aquifers.

    What Are Biosolids?

    When wastewater is processed, solids are separated from liquids, with the solids then being treated to produce a nutrient-rich biosolid. They often sell this “sewage sludge” to farms to be used as fertilizer. 

    Wastewater treatment plants in rural areas also dump a lot of contaminant-rich sewage sludge directly into potential water sources like rivers and streams.

    What Contaminants Are Associated with Agricultural Pollution of Water Sources?

    The drinking water contaminants associated with agriculture include nitrate (from nitrogen fertilizer and manure), pesticides, and emerging contaminants (like PFAS from biosolid applications). Coliform in well water may be a concern in areas near livestock operations, when manure is misapplied to fields, and if there are septic system problems. Heavy metals are often in the makeup of pesticides and fertilizers.

      • Nitrates (& other nutrients)
        High nitrate levels can be harmful, particularly to infants and pregnant women. Nitrogen and phosphorus-rich fertilizers make up a large part of the runoff that leaches into water sources and elevates nitrate levels in drinking water supplies.

        Surveys by the USGS found that one quarter of the shallow wells tested underneath or nearby heavily farmed areas were contaminated above the EPA limit (10 PPM). Almost three quarters of the communities with nitrate levels in drinking water at or above 10 PPM are found in only five states: Arizona, California, Kansas, Oklahoma, and Texas.[1]
      • Bacteria
        In addition to nutrients like nitrates and phosphorus, livestock waste from sprawling animal feed farms is full of potentially harmful coliform bacteria like E. coli, which can travel with runoff into drinking water supplies. Bacteria is always a concern for well owners, but even more so when wells are near animal farms. 

        Furthermore, algal blooms (also a result of an overflow of nutrients from fertilizers and/or manure) are caused by cyanobacteria; cyanobacteria can result in toxins that are harmful to human health if not properly treated.
        • Heavy Metals
          Heavy metal contamination from agriculture is largely due to their presence in certain fertilizers. Analytical testing of some industrial-grade fertilizers have revealed concerning levels of arsenic, cadmium, and lead.[2] Lithium is also found in fertilizers and potash mixtures.

          Analytical testing of both glyphosate-based and non-glyphosate-based pesticides revealed elevated levels of arsenic, chromium, cobalt, lead, and nickel—heavy metals all linked with toxic effects in humans.
        • Pesticides (incl. herbicides, insecticides, & fungicides)
          While pesticides typically contaminate groundwater sources by seeping into the soil, they spread easily too, and end up in water sources through rain, runoff, and wind. These chemicals can stay in groundwater for decades, even if efforts are made to reduce pesticide use above ground.

          Traditionally, insecticides have been considered more harmful to humans than herbicides because of the biological differences between humans and plants. Nevertheless, organophosphate pesticides (which include both herbicides, like glyphosate, and insecticides, like chlorpyrifos) are considered the most harmful pesticides to humans.[3] Some of the more concerning pesticide compounds include:
          • 1,2-Dibromo-3-chloropropane (dibromochloropropane or DBCP, discontinued but environmentally persistent)
          • Atrazine
          • Acephate
          • Chlormequat (a recently introduced pesticide)
          • Chlorpyrifos
          • Dimethoate
          • Glyphosate (or RoundUp, an organophosphate)
          • Paraquat
          • Phosmet
        • Emerging Contaminants (like PFAS and PPCPs)
          Due to their inescapable presence in our everyday lives, PFAS (per- and polyfluoroalkyl substances) end up in wastewater streams nationwide. Because the biosolids that are commonly sold to large farming operations are a product of wastewater treatment, PFAS (which are prohibitively costly to fully remove) find their way into the soil that grows the food we eat, and into ground and surface waters through leaching and/or runoff.

          Other emerging contaminants, including PPCPs (pharmaceuticals and personal care products) can end up in wastewater streams. Likewise, hormones and antibiotics used in the rearing of livestock can find their way into drinking water supplies.

      Other concerns include total suspended solids (TSS)—or sediment—which can carry bacteria and other contaminants, and the way agricultural practices impact water chemistry. For example, pH variations, which can lead to acidic or alkaline conditions, can affect water quality and the effectiveness of water treatment.

      How do coliform bacteria enter well water

      Which Agricultural Contaminants Should I Be Most Concerned About?

      Protecting well water from agricultural pollution is a chief concern, namely because wells are unregulated and solely the responsibility of the well owner. Testing your water once a year is highly recommended, more often if you live close to factory farms.

      Contaminants of Concern: 

          • Nitrates (especially with newborns and small children in the home)
          • Coliform bacteria
          • Heavy metals
          • PFAS 
          • Volatile organic compounds (VOCs), like DBCP
          • Sediment (which can overwhelm catchments, promote bacterial growth, and carry other contaminants)

        Be sure these contaminants are available in your chosen testing kit. Volatile Organic Compounds (VOCs) are also a contaminant class to test for as some pesticides are considered VOCs. VOCs will volatilize from surface water sources, but some VOC pesticides are persistent in soil and can make their way to groundwater.

        Testing specifically for pesticides is an option as well, but pesticides are a broad group of contaminants and the precise compounds tested will depend on the lab’s analytical capabilities.

        Why Is Testing Your Well Water for Agricultural Contaminants So Important?

        Testing your well water is the only way to detect the majority of agricultural contaminants of concern. Nitrates and heavy metals, for example, have no color, taste or smell, so there’s no way to know if these contaminants are in your water. Knowing the precise contaminants in your water—and their concentrations—is a key part of understanding not only your risk factor but your treatment options as well.

        Testing Options for Agricultural Contaminants

        Forwell owners near agriculture who want detailed information on the most common contaminants in their water, we recommend the Advanced Well Water test kit. In addition to coliform bacteria, nitrates, and heavy metals, VOCs and a number of pesticides are included in the list of analytes:

        More specific tests are available if you want to tailor your testing to particular contaminants:

        This pesticide water test includes detailed analysis for common pesticides in drinking water—such as atrazine, simazine, and methoxychlor:

        Testing for the presence or absence of coliform in your well water is a great option if you’re in between annual tests and/or if there’s been a major storm or runoff event in the vicinity of an animal farming operation:

        You can also test your water for PFAS and PPCPs, which can be helpful due to their presence in biosolid fertilizers:

        Contact Tap Score for Unbiased Advice

        Can I Filter Out Agricultural Contaminants from My Drinking Water?

        Yes, thankfully there are a number of ways to filter agricultural contaminants from your drinking water. Precise treatment technologies will depend on the contaminants you’re dealing with and your water supply.

        Anion exchange and reverse osmosis (RO) systems are the most common technologies used to get nitrate out of drinking water.

        As we mentioned above, private well owners should always be on the lookout for coliform bacteria. If your well water is contaminated with coliform bacteria, cease use immediately and have your well shock chlorinated. If you have persistent bacteria issues, UV light could be an addition to your treatment train.

        Filtering bacteria is not recommended.

        Heavy Metals
        Determining your best treatment options will depend on precisely what metals are detected in your water. Lead is best filtered through activated carbon and RO systems that have been certified to NSF/ANSI standard 53 (activated carbon) or 58 (RO) for lead. Arsenic can be removed from drinking water through anion exchange and RO systems. 

        Activated carbon filters that have been certified to NSF/ANSI standard 53 for pesticides are your best bet. Testing your water will help you determine the specific chemical pesticides in your water, which will in turn help you dial in your treatment options. 

        PFAS and PPCPs
        Activated carbon filters, anion exchange, and high-pressure membranes including NF and RO are all effective treatments for PFAS. Activated carbon filters, ozonation, advanced oxidation, NF, and RO are effective against PPCPs depending on the precise compounds.

        Ultimate and Unbiased Guide to the Best Water Filters for Your Home in 2024

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        About The Author


        Sasha Sosnowski is a writer and editor from Los Angeles, California. He studied journalism and history at the University of Warsaw and the University of Arts London and has demonstrated his skills through professional roles as a research assistant, proofreader, magazine editor, and essayist. In his spare time, Sasha enjoys working on his collection of vintage typewriters.
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