Nitrogen is present in the environment inmany forms. The earth’s atmosphere con-sists of 70 percent nitrogen.

When nitrogen interacts with another element in theenvironment, it changes form and becomes a com-pound. Two kinds of nitrogen compounds found innature are nitrates (NO3) and nitrites (NO2). Nitratesand nitrites are chemicals that are made up of nitro-gen and oxygen and that combine with variousorganic (related to or derived from living organisms)and inorganic compounds. Once taken into the body,nitrates are converted into nitrites. Nitrates occur naturally in drinking water. However,if there are high levels of nitrates in the water, it isprobably caused by human activities such as theoveruse of chemical fertilizers and improper disposalof human and animal wastes. These fertilizers andwastes contain nitrogen compounds that are convert-ed to nitrates in the soil. Nitrates dissolve easily in water and can move readi-ly through soil into the drinking water supply. Asnitrate accumulates in water, high levels can buildup over time. For most adults, nitrates are unlikelyto be harmful, even at elevated levels. But ingestingtoo much nitrate can be harmful for very younginfants and susceptible adults.

Who regulates drinking water safety?

In 1974, the United States Congress passed the SafeDrinking Water Act. This law requires the U.S.Environmental Protection Agency (EPA) to determine

Drinking Water Problems: Nitrates

Monty C. Dozier, Assistant Professor and Extension Specialist,Rebecca H. Melton, Extension Assistant,

Michael F. Hare, Senior Natural Resources Specialist Pesticide Programs Division,Janie Hopkins, Manager Groundwater Monitoring Section, Texas Water Development Board,

Bruce J. Lesikar, Professor and Extension Agricultural Engineer, Texas Cooperative Extension,The Texas A&M University System

B-61843-08

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the safe levels of chemicals for U.S. drinking water. The EPA conducts research to determine the level ofa contaminant in drinking water that is safe for aperson to consume over a lifetime and that watersystems can reasonably be required to remove fromdrinking water, given present technology andresources. This safe level is called the maximum con-taminant level (MCL). The MCL for nitrate-nitrogenis 10 milligrams per liter (mg/L), which is commonlyreferred to as parts per million (ppm). For nitrite-nitrogen, the MCL is 1 ppm. The EPA’s drinking water standards—and the regula-tions for ensuring that these standards are met—arecalled the National Primary Drinking Water Regula-tions. All public water supplies must abide by theseregulations. Although private water wells are not required tomeet the national drinking standards, private wellowners can use these standards to monitor the quali-ty of their water. Just as public water suppliers maynot deliver water containing contaminants over theMCL to the public, private well owners should notuse water above MCL levels for human consump-tion.

How are people exposed to nitrate?

Because nitrate is a natural substance found in bothwater and plants, people are exposed to it primarilythrough the diet. In the United States, the averageperson consumes about 75 to 100 milligrams (mg) ofnitrate per day.

blue. This condition results from high nitrite levels inthe blood. Untreated, severe methemoglobinemia can result inbrain damage and even death. Infants in the first 6months of life are particularly susceptible to nitrite-induced methemoglobinemia. Because infants live ona mainly liquid diet, they drink more water for theirweight than do adults and, consequently, they ingesta much higher level of nitrate. Some adults may also be susceptible to nitrite-induced methemoglobinemia. These include preg-nant women with a particular enzyme deficiency,adults with reduced stomach acidity and those witha deficiency in the enzyme needed to change methe-moglobin back to normal hemoglobin, a conditionthat can be hereditary. Fortunately, methemoglobinemia is easily recognizedby the medical and public health communities, andit can be readily diagnosed and treated. Symptomsinclude shortness of breath and blueness of the skin.Research suggests that methemoglobinemia does notoccur in infants when drinking water levels are 10mg nitrate-nitrogen/L (or ppm) or less. This is sup-ported by many research studies in humans. Another concern regarding nitrate ingestion is thatnitrites in the stomach and intestines may contributeto the development of some cancers. Also, lifetimeexposures to nitrates and nitrites can cause an exces-sive discharge of urine, increased starchy depositsand hemorrhaging of the spleen. Nitrate in groundwater is of concern not onlybecause of its toxic potential, but also because it mayindicate that the groundwater is contaminated withother substances. The source of the nitrate may be aclue as to other contaminants that may be present. Ifthe water is contaminated by animal waste or efflu-ent from septic tanks, it may also contain disease-causing bacteria, viruses and protozoa. If the water iscontaminated by fertilizers, it may also contain otheragricultural chemicals besides nitrates, such as pesti-cides.

What happens to nitrates/nitritesin the environment?

In natural waters, most nitrogenous materials tend tobe converted to nitrate. So you should consider allsources of combined nitrogen, particularly organicnitrogen and ammonia, as potential sources of nitrate. The most common sources of nitrate are municipaland industrial wastewaters, refuse dumps, animalfeed lots and septic systems. Commercial fertilizersin rural and urban areas can also be a source ofnitrates in the environment.

About 80 to 90 percent of this amount comes fromvegetables. Vegetables naturally containing high lev-els of nitrates include beets, celery, lettuce andspinach. Some vegetarians have nitrate intakes of upto 250 mg per day. Drinking water generally accounts for 5 to 10 per-cent of the nitrates that people consume. However,in areas where the drinking water is contaminated toa level of 50 ppm)—five times the MCL for nitrate-nitrogen—drinking water may supply as much ashalf of a person’s total daily intake.Nitrate intake depends on a variety of factors, includ-ing diet and the amount and quality of water that aperson consumes. If there are high levels of nitrite inthe body, it is generally because of high levels ofnitrates in the drinking water. Some adults who eat many vegetables and drinkwater containing high levels of nitrate (up to 10 mgnitrate-nitrogen/L) could take in as much as 1.6 mgof nitrate-nitrogen per kilogram of material con-sumed per day. This is the estimated highest dose ofnitrates that a person can take in every day withoutharm.

What are the health effects of nitrates/nitrites?

Nitrate becomes toxic primarily when bacteria in ourdigestive system convert it to nitrite. The nitrite oxi-dizes iron in the hemoglobin of our red cells to formmethemoglobin. Hemoglobin transports oxygen through the body.However, methemoglobin cannot bind oxygen and,therefore, cannot supply oxygen to the body. Whenhemoglobin is converted into methemoglobin, thebody cannot get the oxygen it needs to function well.This results in a medical condition known as methe-moglobinemia. Low levels of methemoglobin occur normally in peo-ple, with typical values usually ranging from 0.5 to2.0 percent. Because the blood has extra capacity tocarry oxygen, a person can have methemoglobin lev-els of approximately 10 percent with no significantsymptoms of illness.If methemoglobin levels rise above 10 percent, a per-son’s skin and lips may turn bluish. Levels above 25percent can lead to weakness, rapid pulse and rapidbreathing. Levels over 50 to 60 percent can causedeath. The most significant health effect associated withnitrate ingestion is methemoglobinemia in infantsunder 6 months old. Methemoglobinemia is oftencalled “blue baby syndrome” because the affectedinfant’s fingers, toes, arms and legs begin to turn

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Once nitrate is formed, its movement in soil andpotential to contaminate groundwater depends onseveral factors, including the soil characteristics, soiltexture, the depth and characteristics of the under-ground water formations (aquifers), and climaticrainfall conditions. The potential for nitrate contami-nation of drinking water also depends on the depthand construction of wells. Many factors can make it difficult to identify thesource of nitrates for an individual well. Becausenitrates move with the flow of groundwater, thesource may be far from the well. The amount oftime it takes for nitrate to pass through the soil intogroundwater is affected by many variables, includingthe chemical’s application rate, the soil type and thedepth of the soil to the water table. The water tableis the top of the groundwater formation, or the pointwhere the saturated zone on the soil surface begins.

Where in Texas have wells with high levels of

nitrate been found?In Texas, groundwater quality is monitored by sever-al agencies, including the Texas Water DevelopmentBoard (TWDB), which collects groundwater samplesthrough its Groundwater Quality Sampling Program. From 1988 to 2004, TWDB staff collected 24,272 sam-ples from 11,501 wells for nitrate (Fig. 1). Of thosesamples:

• 16 percent contained no detectable amounts ofnitrate.

• 20,498 samples contained detectable amountsof nitrate, averaging 4.0 milligrams/liter (mg/l).

• 1,141 samples, or 5 per-cent of the total samplepopulation, contained lev-els of nitrate above the pri-mary MCL of 44.3 mg/l. Note:The MCL for nitrates alone is 44.3mg/L or ppm. The MCL for nitrate-nitrogen is 10 mg/L or ppm.

High levels of nitrate (over the MCL) werefound in 24 of the 31 major and minoraquifers (Figs. 2 and 3). One household well inthe Yegua aquifer and one industrial well inthe Marathon aquifer contained nitrate detect-ed at 63 mg/l and 64 mg/l respectively. The two aquifers having the most wells withexcess nitrate were the Ogallala, with 278 wells(401 samples), and the Seymour, with 138 wells(185 samples). The highest nitrate values werefound in two aquifers: the Seymour, where a

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sample from an unused well contained 1,484 mg/l,and the Dockum, where a sample from a stock wellcontained 244 mg/l. Other aquifers in which a significant number of sam-ples (and wells) contained excessive nitrate were theEdwards-Trinity High Plains (62 samples), theDockum (60 samples) and the Trinity (65 samples).Eleven of the 24 aquifers with high nitrate containedwells from which no more than 10 samples wereover the standard. Of the 1,141 samples from wells with high nitrate:

• About 47 percent came from wells that sup-plied water to households.

• 20 percent came from irrigation wells.• 13 percent were from wells supplying livestock.• 10 percent were from public supply facilities.• 4 percent from wells with other uses.• 6 percent were from unused wells.

Nitrate ( as NO3) concentrations

Not detected

0.01 to 44.29 milligrams/liter

44.3 milligrams/liter and greaterN

0 50 100 160 200 Miles

Figure 1. Nitrate concentrations in Texas water wells 1988-2004.

How are nitrates/nitritesdetected in drinking water?

The regulation for nitrates/nitrites became effec-tive in 1992. Between 1993 and 1995, the EPArequired water suppliers to collect water samplesat least once a year and analyze them to find outif nitrates/nitrites are present above 50 percent oftheir MCLs. If nitrates/nitrites are found abovethis level, the system must continue to monitorthis contaminant every 3 months.If contaminant levels are found to be consistentlyabove the MCLs (10 ml/L or ppm for nitrate-nitro-gen and 1 mg/L or ppm for nitrite-nitrogen), watersuppliers must take steps to reduce the amount ofnitrates/nitrites to bring them consistently belowthat level. The suppliers must also notify the pub-lic about the problem via newspapers, radio, TVand other means. They may be required to takeadditional actions, such as providing alternativedrinking water supplies, to prevent serious risks topublic health.

How is nitrate removedfrom drinking water?

Homeowners using public or private watersupplies may choose to treat their water toremove the nitrate before use. The EPA hasapproved three treatment methods for remov-ing nitrates/nitrites: ion exchange, reverseosmosis and electrodialysis.

Reverse osmosisThe most common treatment method fornitrate in a water supply is reverse osmosis(RO). This method is cost effective for a homethat uses only a few gallons of water forhuman consumption per day. The more drink-ing water a household uses, the more expen-sive the treatment. Most RO units have five components:

• A prefilter to remove solids and extendmembrane’s life

• An activated carbon filter to removeodors, flavors and chlorine

Figure 2. Major Aquifers of Texas.

Ogallala

Gulf Coast

Edwards (BFZ)

Carrizo - Wilcox

Trinity

Edwards - Trinity (Plateau)

Seymour

Hueco - Mesilla Bolson

Cenozoic Pecos Alluvium

Bone Spring — Victorio Peak

Dockum

Brazos River Alluvium

Edwards — Trinity (High Plains)

West Texas Bolsons

Queen City

Woodbine

Hickory

Blaine

Sparta

Nacatoch

Lipan

Blossom

Marble Falls

Capitan Reef Complex

Rita Blanca

Ellenburger — San Saba

Rustler

Igneous

Marathon

Figure 3. Minor Aquifers of Texas.

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• A semipermeable membrane through whichwater flows under pressure; the most effectivetreatment to remove nitrate using an RO sys-tem is a thin film composite membrane

• A tank to hold the treated water• A drain connection for discharging the waste-

water produced by the treatment processThe RO unit operates by passing water under pres-sure though a semi-permeable membrane (Fig. 4).The membrane allows water to pass through butblocks the nitrate. You can improve the nitrateremoval in this system by increasing the water pres-sure with a booster pump.

The RO membrane must be replaced according tothe manufacturer’s recommended schedule. Newmembranes cost about $150, and a carbon-based pre-filter typically costs between $15 and $50. Depending on the system and based on a 10-year lifeof the system, the cost of treating the water rangesfrom 5 to 10 cents per gallon produced. This estimatedoes not include the cost of the wasted water or thecost, if any, of treating the wastewater. Remember to always check and replace all filters asneeded. If used filters are not changed when needed,they can reintroduce previously filtered nitrates backinto the water system and actually increase the con-centrations of nitrates in the water.

DistillationDistillation removes nitrate from water without wast-ing water. In the distillation process, water is heatedto boiling in an enclosed container (Fig. 5). As thewater evaporates, the impurities in the water are leftbehind. The steam then cools and condenses backinto a liquid. Some of the dissolved gases and compounds from thewater will also be carried up with the steam andtherefore end up in the treated water. These contami-nants can be removed by passing the distilled waterthrough a post filter. Most units will treat 5 to 11 gal-lons of water a day.

Figure 4. Reverse osmosis treatment unit (Adaptedfrom Kneen et al., 1995 and USEPA, 2003).

The disadvantage of an RO unit is the small amountof consumable water produced. Most units achieveonly 20 to 30 percent water recovery, meaning thatof 100 gallons treated, only 20 to 30 gallons will beusable. The rest of the water is sent to the waste-water treatment system. Homeowners using on-sitewastewater treatment systems should consider theeffect that the additional loading may have on theirseptic systems. Because of the RO system’s inefficiency, it is typi-cally used to treat only drinking and cooking water.When choosing the size of the system to buy, baseyour decision on the number of gallons to be usedfor these purposes each day. The typical unit pro-duces from 5 to 15 gallons per day.

Cost

Typical RO devices cost from $200 to $1,000. Thedevice takes about 30 to 60 minutes to install, assum-ing no significant plumbing modifications are needed.

Figure 5. Distillation process (Adapted from Kocher etal., 2003).

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Cost

The operating costs for distillation may be higherthan other treatment methods because of the amountof electricity needed to operate the distiller. Use thisformula to estimate the cost of energy:

Wattage of unitCost/gal = 0.024 x x cost of electricity ($/kWh)

Production (gal/day)

Distillation units can be purchased for $300 to $1,200.

Ion exchangeA good option for treating large amounts of water ision exchange. Ion exchange removes nitrates fromwater by passing it under pressure through one ormore columns packed with a compound called anexchange resin (Fig. 6).

Another major concern when using ion exchangetreatment is a phenomenon called chromatographicpeaking. When chromatographic peaking occurs, thewater leaving the column will have higher concen-trations of nitrate than will the water entering thecolumn. Peaking should not occur if a nitrate-selective resinis used. Peaking is most often seen when the watersource contains sulfate and the column is beingoperated past saturation. Chromatographic peaking and other problems canerupt quickly in ion exchange units. Because of this,you should check the water supply often to makesure the unit is working properly if your unit uses aresin that is not nitrate-selective. Another factor that significantly affects nitrateremoval is flow rate. A good flow rate for an ionexchange system is 2.5 gallons/cubic foot/minute. When buying a system, be sure to select one that isappropriate for residential use. Take care to not mixthe nitrate resin with water softener resin.

CostIn addition to the cost of monitoring and resinreplacement, the initial cost for an ion exchangeunit ranges from $400 and $1,500.

ElectrodialysisElectrodialysis removes nitrates by feeding waterthrough several stacked membranes that alternate inselecting anions (negatively charged ions) andcations (positively charged ions) (Fig. 7). Nitrate ionsare drawn through the membrane pores with elec-trical currents. The nitrate is pulled from the waterinto a brine waste stream.

Nitrate-contaminatedwater

Treatedwater

Nitrate

Chloride or hydroxide

Exchange resin

Figure 6. Ion Exchange Process (Adapted fromRobillard et al., 2001).

This system works like a water softening system. Asnitrate moves across the resin, an ion is releasedfrom the resin. The nitrate leaves the water and takesthe place of the ion in the column. After all the origi-nal ions have been replaced, the column is saturatedwith nitrate and must be regenerated or replaced. A disadvantage of ion exchange systems is the cost ofrecharging the resins. To treat water for nitrates, theresins can be recharged only at special facilities,which makes treatment by ion exchange expensive. If the column is not regenerated or replaced, nitratewill be dissolved back into the water system. Thiscan actually increase the nitrate concentration of thewater.

Figure 7. Electrodialysis Process (Adapted from GE,2005).

+–

++++

++ + +

+

– – – –

–– –

–

–

–

+ +

+

–

– –

Anode

Anion-exchange membrane

Cation-exchange membrane

Anion-exchange membraneCation-exchange membrane

Concentratedwater

Treated water

Concentratedwater

Concentratedwater

Treated water

Cathode

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The drawbacks to using electrodialysis for homewater treatment are that the process is complicatedand costly, and sometimes local codes prohibit it fornitrate removal.

How to select a treatment unitBecause no single technology can treat all water con-taminants, you should have your water tested by aqualified laboratory before selecting a treatmentoption. For a list of labs certified by the TexasCommission on Environmental Quality (TCEQ) totest drinking water, visit http://www.tnrcc.state.tx.us/permitting/waterperm/pdw/chemlabs.pdf. Once you have established what is in the water,research the different products on the market andfind one suitable for treating the constituents in yourwater supply. Compare the initial, operation andmaintenance costs and requirements, contaminantremoval efficiency, warranties, life expectancy of thesystem and the reputation of the company. Also con-sider the wastewater or solid waste that the systemwill generate in your final decision. For more information on the types of in-home watertreatment options for specific contaminants, refer tothe Drinking Water Problems series of publicationsby the Texas AgriLife Extension Service. They areavailable at http://AgriLifebookstore.org.It is important to note that home water treatmentsystems are not regulated by federal or state laws.However, some national organizations do certifywater-treatment products:

• The Water Quality Association (WQA) offers avalidation program and advertising guidelines.Products that receive a Gold Seal ProductValidation from the WQA are certified in theirmechanical performance but not in their abilityto remove harmful contaminants.

• The National Sanitation Foundation (NSF) certi-fies products that can remove contaminantsaffecting health. For a list of drinking watertreatment units that have NSF certification,visit http://www.nsf.org/Certified/DWTU. If you have questions about whether a particu-lar product is certified, contact the NSFConsumer Hotline at 877-8-NSF-HELP orinfo@nsf.org or by writing to: NSFInternational, NSF International, P.O. Box130140, 789 N. Dixboro Road, Ann Arbor, MI48113-0140.

Please note: If a product has an EPA registrationnumber, this merely indicates that the unit is regis-tered with the EPA. It does not imply EPA approvalor certification.

How to keep it workingNo matter what treatment technology is being used,some sort of maintenance will be required to keepthe system operating properly. The first step to prop-er operation and maintenance is proper installation.Qualified installers:

• Carry liability insurance for property damageduring installation

• Are accessible for service calls• Accept responsibility for minor adjustments

after installation• Give a valid estimate of the cost of installation

After your system is installed, it will need to bemaintained properly. If you have an RO unit, replacethe membranes as necessary. Periodically removescales and other solids that collect in the still and dis-pose of them properly.For ion exchange units, replace or recharge the resinregularly. Maintain and change all filters as needed.All systems should be operated according to themanufacturers’ specifications. If a system treats morewater than it is designed for in a certain period, thetreatment may be ineffective and quality of the treat-ed water may drop.Treated water should be tested regularly to ensurethat the system is operating properly. The best timesof the year to test for nitrate concentration is in thespring and fall because nitrate is typically the highestin raw water sources then. Although new home-based tests are better than thosepreviously used, the best way to have water tested isby a certified lab. For a lab in your area, consult yourlocal health department, the county office of TexasCooperative Extension or the TCEQ’s list of watertesting laboratories mentioned earlier.

For more informationArsenic Treatment Technology Evaluation Handbook forSmall Systems. EPA 816-R-03-014. United StatesEnvironmental Protection Agency (USEPA). 2003.Available at http://www.epa.gov/ogwdw000/smallsys/arsenic_treatment_handbook_lo.pdf. “Choosing home water treatment devices,” WaterFacts: Number 7. Arizona Cooperative Extension.Available at http://ag.arizona.edu/pubs/water/az9420.pdf.“Drinking Water Treatment: Distillation.” NebraskaCooperative Extension. Available at http://ianrpubs.unl.edu/water/g1493.htm.“Electrodyalisis.” GE Infrastructure Water & ProcessTechnologies. General Electric. 2005. Available athttp://www.ionics.com/technologies/ed/index.htm.

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“A Guide to Home Water Treatment.” MichiganState University Extension. Available athttp://www.gem.msu.edu/pubs/msue/wq21p1.html.Harmon, S. 2002. “Nitrate removal: Searching forthe ideal in an imperfect world.” Water TechnologyOnline. Available at http://www.watertechonline.com/article.asp?IndexID=6633204.“Home Drinking Water Treatment Systems.” NorthCarolina Cooperative Extension Service. Available athttp://dwb.unl.edu/Teacher/NSF/C01/C01Links/www2.ncsu.edu/bae/programs/extension/publicat/wqwm/he419.html.Lahlou, M. Z. “Point-of-Use/Point-of-Entry Systems.”Morgantown, WV: National Drinking Water Clear-inghouse. 2003. Available at http://www.nesc.wvu.edu/ndwc/articles/OT/SP03/TB_Point_of_Use.html.

“Water Quality: Distillation.” Kansas State UniversityCooperative Extension Service. Available at http://www.oznet.ksu.edu/library/H20QL2/MF885.PDF.“Water Softening.” Penn State Cooperative Extension.Available at http://www.sfr.cas.psu.edu/water/water%20softening.pdf. “Water Treatment Notes: Reverse Osmosis Treatmentof Drinking Water.” Cornell University CooperativeExtension. Available at http://www.cce.cornell.edu/fact-sheets/wq-fact-sheets/FSpdf/Factsheet4.pdf.

AcknowledgmentsGuidance and assistance was provided by the TexasGroundwater Protection Committee and the TexasCommission on Environmental Quality. The effortwas partially funded by the U.S. EnvironmentalProtection Agency.

This publication was funded by the Rio Grande Basin Initiative administered by the Texas Water Resources Institute ofthe Texas AgriLife ExtensionService, with funds provided through a grant from the Cooperative State Research, Education,and Extension Service, U.S. Department of Agriculture, under Agreement No. 2005-45049-03209.

age, or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as ammend-ed, and June 30, 1914, in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas AgriLifeExtension Service, Texas A&M System.2M, Reprint