Sometimes hot water will have a “sour” smell,similar to that of an old damp rag. This smell oftendevelops when the thermostat has been lowered tosave energy or reduce the potential for scalding.Odor-causing bacteria live and thrive in warmwater and can infest the water heater. The problemfrequently can be corrected by returning thethermostat to its recommended operating tempera-ture (approximately 160 degrees F) for 8 hours.This will kill the bacteria. (Caution: Be sure thewater heater has an operable pressure relief valvebefore increasing the temperature, and warnoccupants of the scalding hazard.) If a lower tem-perature is preferred for routine operation, periodichigh temperature flushing can be used wheneverthe odor returns.

Testing for hydrogen sulfideThe cause of the hydrogen sulfide problem must

be determined before proper testing and appropri-ate treatment can be applied. If the problem iscaused by hydrogen sulfide in the groundwater,then the concentration of the gas in the water mustbe measured in order to select and properly size atreatment system. Hydrogen sulfide gas dissolvesreadily in water and can readily escape from it(volatilize). Thus, water samples must be tested on-site, or immediately stabilized for laboratoryanalysis. Sample bottles withstabilizing chemicals shouldbe obtained from the labora-tory that does the analysis.Careful sampling accordingto laboratory recommenda-tions is critical to ensureaccurate and reliable results.In general, the requirementswill involve delivery of arefrigerated sample within48 hours of collection. Sulfideconcentrations are reportedby laboratories in units ofmilligrams per liter (mg/l) orparts per million (ppm).These two terms are usedinterchangeably.

If the gas is being pro-duced by an active colony ofsulfur-reducing bacteria, thismust be determined. Activecolonies could be locatedanywhere within the plumb-ing system, well casing or inthe aquifer. Selected commer-cial water testing laborato-ries can determine thepresence of sulfur-reducing

bacteria. If the bacteria are detected, treatment tocontrol the bacteria should eliminate the problem.

Other contaminants (sulfate, organic compoundsand metals) can cause taste and odor problems indrinking water. Water tests should always beconducted on new wells or when problems aresuspected in an existing water supply. This can beparticularly important if more than one contami-nant is involved because it will affect properdiagnosis of the problem and selection of the mosteffective and economical water treatment system.

Treatment options forhydrogen sulfide

The recommended treatment to remove hydro-gen sulfide from a water supply depends largely onthe gas concentration.

Trace amounts of hydrogen sulfide (0.05 - 0.3 mg/l)

Activated carbon adsorbs soluble organic com-pounds and certain gases, such as chlorine andhydrogen sulfide, that contribute tastes and odorsto a water supply. Very small amounts of hydrogensulfide can be removed from water with activatedcarbon filters (Fig.1). Activated carbon is used as agranular form in tank-type filters and as finelydivided powder in a cartridge. The hydrogen sulfideis adsorbed onto the surface of the carbon particles.

Figure 1. Point-of-use and point-of-entry placements of activated carbonfilters.

2

Filter

Hot

ColdFilter

Hot

Cold

In-Line

Filter

Hot

Cold Water MeterFilter

Point-of-Entry (POE)

To HouseholdPlumbing

NonhouseholdPlumbing

Line Bypass

Faucet Mount

Some filters will improve taste, but will not elimi-nate unpleasant odors. A granular filter must bebackwashed periodically; a cartridge filter must becleaned or replaced periodically. Cleaning frequencydepends on the amount of hydrogen sulfide in thewater and the volume of water treated. Moderate tohigh levels of hydrogen sulfide will require frequentfilter replacement. These filters also can removetannins and other dissolved organic compounds.

Less than 2 mg/l hydrogen sulfide

Aeration (adding air to the water) is a treatmentoption for this concentration range, and is commonlyused by city water treatment systems. Oxygen in theair reacts with hydrogen sulfide to form an odorless,dissolved form of sulfur called sulfate. Several typesof aeration systems are available. In one type,compressed air is injected into the water system.The air then must be removed from the water toprevent knocking or air-blocks in the system and toreduce the corrosion potential caused by dissolvedoxygen. In another type, water is sprayed into anonpressurized storage tank (Fig. 2). A second pumpis needed to re-pressurize the water. The storagetank provides 6 to 8 hours holding time for oxidationof hydrogen sulfide, iron and manganese. Thestorage tank and aerator must remain secure toprevent contamination of the water supply, or thesystem must be chlorinated. This process usuallyproduces a strong hydrogen sulfide odor near theaerator, and may not always reduce the hydrogensulfide to nondetectable levels. In such cases, acarbon filter can be used to remove some of theremaining trace amounts of hydrogen sulfide.

These complex systems are not recommendedfor household use.

Figure 2. Nonpressurized aeration system from hydrogen sulfide removal.

3

ProductWater

Second PumpWell Pump

Well Pressure Tank

Gate/Ball Valve

Aerator/Degasifer

Check ValveSecond Pressure Tank

To Well

Up to 10 mg/l hydrogen sulfide

An iron removal filter containing manganesegreensand can remove low to moderate levels ofhydrogen sulfide in addition to iron and manga-nese. The process oxidizes hydrogen sulfide intosulfate; iron and manganese form precipitates thatare filtered out (Fig. 3). Manganese greensandfilters must be recharged with a solution of potas-sium permanganate when the oxygen is depleted.This process is very similar to the regenerationprocess used in water softeners, and must beperformed at regular intervals of 1 to 4 weeksdepending on the chemical composition of thewater, size of the unit and amount of water pro-cessed. Water with a pH below 6.7 could requireacid neutralization, increasing the pH to 7.5 to 8.3,before iron removal will be effective. These filtersystems are very specialized and the installationand operation instructions of the manufacturershould be followed precisely.

Figure 3. Manganese greensand pressure filtrationsystem for removal of hydrogen sulfide, iron andmanganese.

Regeneration Unit

From Well

To House

ManganeseTreated Greensand

GravelFilter

KMnO4 Feed Tank

KMnO4 Solution

Up to 75 mg/l hydrogen sulfide

Continuous chlorination using an automaticchemical feed pump can effectively remove mediumto high levels of hydrogen sulfide (Fig. 4). Chlorinequickly oxidizes hydrogen sulfide into a tasteless,odorless form. Continuous chlorination also effec-tively removes iron and manganese that can occurin association with hydrogen sulfide.

Chlorine demand (concentration) and contacttime are very important to successful chlorination.The amount of chlorine needed to react withorganic and inorganic materials in the water canrange from 1 mg/l to more than 10 mg/l if the wateris high in sulfide, ammonia, iron or manganese.Table 1 presents typical dosages required to treatspecific problems.

Contact time (exposure) depends on the concen-tration of chlorine in the water, water temperatureand pH. Oxidation of iron and hydrogen sulfide isinstantaneous, while manganese oxidizes moreslowly. Chlorine should be introduced into thesystem before it reaches the storage tank. The tankmust have sufficient volume to provide a 20-minutecontact time between the water and the chemical.In addition, a fine-retention sediment filter can beused to remove any oxidized iron and manganese.

Excess free chlorine is undesirable and canproduce an objectionable taste in the water. Anactivated carbon filter can be used to obtain chlo-rine-free water for cooking and drinking.

Controlling hydrogen sulfidebacteria in wells

Shock chlorination can effectively eliminatehydrogen sulfide when the problem is caused by thepresence of sulfate- and sulfur-reducing bacteria inthe plumbing system. Shock chlorination uses a

Figure 4. Chlorine injection system for removal of hydrogen sulfide.

4

Chlorinator

CheckValve

ChlorineSolution

Pump

Well

Pressure Tank

Pipe Coil

Table 1. Approximate Chlorine Dosage for Oxidationof Selected Minerals Based on Concentration (mg/l).

Manganese 1.3 times Mn concentration (mg/l)

Iron 0.64 times Fe concentration (mg/l)

Hydrogen Sulfide 2.2 times H2S concentration (mg/l)

single high dose of chlorine placed in direct contactwith water and the plumbing system. Chlorine, ifused in sufficient concentration and with adequatecontact time, is an excellent disinfectant that killsmost disease-causing bacteria, viruses and cysts ofprotozoans. It also kills nonpathogenic iron, manga-nese and sulfur bacteria.

In some cases, iron and sulfur bacteria are moreresistant to chlorine because they occur in thicklayers and are protected by a slimy secretion. Ifproblems with hydrogen sulfide persist after twoattempts at shock chlorination, continuous chlori-nation could be required.

Concentrations of chlorine used in shock chlori-nation are 100 to 400 times the amount found intreated “city water.” The amount of chlorineneeded is determined by the amount of waterstanding in the well. Table 2 lists the amount ofordinary household bleach (5.25 percent hypochlo-rite) needed for shock chlorination based on casingdiameter and water depth in the well. If the depthof the water in the well is unknown, use a volumeof bleach equal to two times the 150-foot depth forthe appropriate casing diameter. For example, an 8-inch casing diameter with unknown water depthwould require 3 gallons of household bleach. Do notuse bleach in excess of the recommended amountbecause it is not necessary and will require addi-tional flushing before household use.

Table 2. Amount of chlorine needed for shock chlorination.

Depth of Casing diameterwaterin well 4-inch 6-inch 8-inch 10-inch 12-inch

10 feet 1/2 cup 1 cup 1.5 cups 1 pint 2 pints

25 feet 1 cup 1 pint 2 pints 3 pints 4.5 pints

50 feet 1 pint 1 quart 2 quarts 3 quarts 1gallon

100 feet 1 quart 2 quarts 1 gallon 1.5 gallons 2 gallons

150 feet 3 pints 3 quarts 1.5 gallons 2 gallons 3 gallons

The procedure for treatment is as follows:1. Dilute the bleach with water in a 5-gallon

bucket. This increases the volume. Pour thesolution around the sides of the well casing.

2. Connect a garden hose to a nearby faucet andwash down the inside of the well.

3. Do not operate the water system for 2 hours.4. Next, open each faucet one by one and allow

water to run until a strong odor of chlorine isdetected. If the odor is not detected, check therate from Table 2 and add more chlorine to thewell, repeating steps one through three.

5. Do not operate the water system for at least 12to 24 hours.

6. Next, flush the system of remaining chlorine.Begin by turning on outside faucets and lettingthe water run until the chlorine smell dissipates.Let the water run on the ground to reduce theload on your septic system. High loads of chlo-rine in the septic tank can kill beneficial bacteriaand require re-inoculation of the septic system.Also, do not apply water with high chlorine

5

levels to lawns, gardens or other sensitive plantsbecause injury can occur.

7. Finally, turn on the indoor faucets until thesystem is completely flushed.

SummaryHydrogen sulfide in drinking water is a common

nuisance contaminant. Although it is generally nota health hazard, the offensive odor and corrosivityof water containing hydrogen sulfide usually maketreatment necessary. Various treatment alterna-tives exist; however, chlorination is the mostcommon and effective method. Iron and manganesefrequently occur in association with hydrogensulfide, and chlorination is an effective treatmentfor removing all three of these nuisance contami-nants. Table 3 presents a summary of treatmentoptions with estimated cost ranges and associatedbenefits. Always compare installation and mainte-nance costs and efficiencies of appropriate treat-ment alternatives and use qualified professionalsfor installation and service.

Table 3. Treatment options for removal of hydrogen sulfide.*

Treatment Type Cost Treatment Range Comments

Disposable carbon cartridge $25-100 <1 ppm Requires regular replacement.

Air purge systems +$600 <20 ppm Requires sizeable equipment placed awayfrom residence. Chlorination of watercould be required in some cases. Notrecommended for hard water.

Oxidizing carbon filter $800-1,200 <2-4 ppm Can be used in conjunction systems withchlorination systems to remove allhydrogen sulfide greater than 2 ppm inwater.

Greensand/Potassium Permanganate $1,200-1,400 <10 ppm System requires regeneration of oxidizingmedia. Chemicals can be messy andunpleasant.

Chlorination systems $900-1,800 <75 ppm Upper cost range assumes removal ofchlorine using a carbon filter system.

*(Based on informal survey of water treatment/equipment suppliers in November 1998)

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, andJune 30, 1914, in cooperation with the United States Department of Agriculture. Chester P. Fehlis, Deputy Director, Texas Agricultural ExtensionService, The Texas A&M University System.

Educational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.

Produced by AgriLife Communications and Marketing, The Texas A&M University System

Extension publications can be found on the Web at: http://AgriLifeBookstore.org.

Visit Texas AgriLife Extension Service at http://AgriLifeExtension.tamu.edu.