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Expert water treatment is essential for managing potable water and ensuring that it’s free from waterborne bacteria and pathogens. To protect the health and safety of all who are impacted by a potable water source, Guardian works with building and facility managers to test water, develop prevention and remediation plans, and implement the proper chemical products and equipment to most efficiently and effectively control waterborne pathogens. 

Proactive Legionella treatment for the prevention of Legionnaire’s Disease

Guardian is a steadfast resource for assisting facilities in creating and implementing all aspects of a Legionella treatment program.  Our Guardian team includes Certified Water Technologists and highly trained technicians who work in partnership with HC Info, a leading Legionella consulting group. Guardian has extensive experience in developing and implementing Legionella treatment programs that prevent Legionella growth and contamination and meet the ASHRAE 188-2018 Standard for risk management.

Guardian Legionella Treatment

If your building or facility needs support to comply with the ASHRAE standard, Guardian can help you address potable and non-potable water sources, including cooling towers, fountains, whirlpools, and other locations where water may potentially harbor Legionella.

Program Team

Individuals designated by the owner or owner’s representative to develop, implement, and maintain the WMP

Verification & Monitoring

Initial and ongoing confirmation that the WMP is being executed as written

Building Survey

List and diagrams of building water systems and equipment

Testing & Validation

Initial and ongoing confirmation that conditions are effectively controlled as stated in the WMP

Water Management Plan (WMP)

Detailed plan for each affected water system, including control measures and corrective actions


Data collection, online resources, and recordkeeping to demonstrate compliance with the standard

Legionella Resources:

In addition to assisting clients with creating a Legionella treatment plan, Guardian is committed to educating building owners and operators about Legionella and proper safety procedures for air conditioning and cooling tower maintenance. We offer a wide variety of free, downloadable resources in our Training Library with topics that include:

Legionella FAQ

What Is ASHRAE 188-2018?

The American Society of Heating, Refrigerating and Air Conditioning (ASHRAE) Standard 188-2015 provides details and guidance to prevent and mitigate the emergence of the bacteria that causes Legionellosis in water systems. Compliance to Standard 188–2015 will be handled by agencies directly involved with assuring the safety of building occupants, including OSHA and The Joint Commission.

What Is a Water Management Program?

A Water Management Program (WMP) is a document describing your facilities “Program” of risk management for potable and non-potable water (e.g. cooling towers, fountains, whirlpools) where water mists may harbor Legionella.

Air Conditioning Maintenance

Where air conditioning units are present, it is important to clean the coils of the units annually to remove grime and oils that can act as incubation sites for Legionnaire’s Disease. In addition, the drip pan for the unit must be maintained in a clean state. Drip pan biocides are available from numerous janitorial supply houses. Place the slow dissolve tablets in the pan and renew as needed. The tablet will keep the pan clean and add a biostat to the pan to deter the growth of bacteria as Legionella.

Cooling Tower Maintenance

  1. Drain the entire system, including connecting piping.
  2. Using a hose, wash down and flush out any foreign material from the cooling tower itself, wash down to the lowest point of the piping, and drain it again.
  3. Make sure that the fans are turned off during the sanitizing and flushing steps that follow. Allowing the fans to run can cause system water to mist, and if Legionella is present, it could cause contamination and contact before the oxidizer is able to kill it. Therefore, during all of the following stages, contain the airflow in the system.
  4. Fill the system with fresh water and then add an oxidizing biocide: chlorine dioxide (0.5 – 1.0 ppm), bromine (0.5 – 2.0 ppm), or chlorine (5.0 – 10.0 ppm) in that order of preference, to the system. In the case of chlorine chemistry, you should not exceed a pH of 8.0, or the efficacy of the chlorine will be dramatically reduced. Circulate this solution for 2 – 24 hours, based on the level of fouling in the system and the past history of the system in regard to corrosion rates, and if Legionella was ever identified in the system. If the cooling tower is a known site of Legionella infection, initial cleaning should follow the Wisconsin Protocol.
  5. Add a penetrant to improve the kill with the oxidizer. This can be a detergent such as Cascade, or a biocide penetrating agent. Circulate the penetrant with the oxidizing biocide.Where corrosion is a concern and where chlorine is to be used, use a blend of phosphate and chlorinated phosphate to the system, or a penetrant with corrosion inhibition properties. These types of products will allow the introduction of the chlorine to the system, while adding a corrosion inhibitor for the system metal surface. Circulate this solution for up to 24 hours, and then dump the system. Test for free chlorine, and when the levels are below 1 ppm, you have flushed the system sufficiently to start up for the season.
  6. Whichever oxidizer is used, dump and flush out the system, refill and initiate the water treatment program.
  7. This procedure should be performed in the Fall and in the Spring, even if the cooling tower is seasonal and is to be shut down for the season.

Seasonal Shutdown of the Cooling Tower

  1. If a cooling tower system is to be shut down, it should be treated with a clean-up prior to being shut down, and then again to a clean-up when it is brought back online in the Spring.
  2. Once the clean-up has been performed, drain the system for the season. If the system is not to be used, it must be drained. This means that the entire system is to be drained, including all of the piping. Any piping left filled with stagnant water over a period of months can culture bacteria like Legionella, so drain it out to prevent the potential for a problem.
  3. In many cases, after the sanitizing of the system, you may wish to circulate a passivating agent containing phosphonates and gluconate before the final draining of the system. This can reduce the potential for surface corrosion while the system is down.

Cooling Tower System Operation

  1. Maintain sufficient bleed in the cooling tower to prevent deposition. Contact your water treatment supplier for the proper inhibitors for your area.
  2. Routinely, at a minimum weekly, check the low flow areas of the cooling tower and manually sweep any sludge buildup away. This prevents the formation of sulfur-reducing bacteria, removes a habitat for the Legionella to grow, and improves the contact of the biocide in the water. Biocides do not penetrate sludge very well.
  3. Add a product to penetrate the biofilm in the system. Up to 98% of the Legionella in a system can be found in the biofilm, instead of in the water. This means that even if you have a biocide that kills on contact in the water, it can only kill about 2% of the Legionella in the system, if it cannot penetrate the biofilm.Penetrants are: DTEA, Chlorinated paraffin/limelidene, DMAD, ethoxylated alcohol-based products.Biocides are: Isothiazolin, DBNPA, Tris Nitro, Bronopol, Glutaraldehyde, Chlorine Dioxide (due to its slow oxidizing reaction) and any blended biocide that uses a penetrating agent.Oxidizing biocides used in conjunction with the above are: Chlorine Dioxide, Chlorine, Bromine, and Hydrogen Peroxide (usually used with Peracetic Acid).
  4. In most cases, it requires more than one biocide to keep a system clean. It is important that biocides are to be used at all times while the cooling tower is in operation. A lack in biocide feed will result in a potential for any bacteria to grow. A cooling tower is a dynamic system, which is constantly infecting itself from the incoming air.
  5. Removal of algae is important for the prevention of Legionella. Algae will provide Legionella with enzymes needed for growth. Therefore, the removal of algae will reduce the potential for Legionella growth.Cover all distribution decks. This will cut off sunlight to the internals of the cooling tower. Algae growth through photosynthesis, so removing sunlight will reduce the potential for their growth.Manually wash off algae that have grown on the exterior of the fill. As a cooling tower operates, mist flows out over the fill. Evaporation of this mist occurs, leaving behind solids from the cooling water. These solids contain organics, which can now be used by Legionella bacteria that pass over the solids with the incoming air as a food source. Algae can also form, as there is moisture, food, and sunlight at this point. Most biocides do not carry out of the system, so a cooling tower that has good in-system control can have a problem on the fill. Tris Nitro has been found to carry to a limited degree out over the fill and dramatically reduce this problem. Manually washing down the fill periodically will also reduce the potential of system contamination.
  6. Testing for biological fouling is also recommended. The standard tests for biological growth are usually culture pads or dipsticks. These are incubated for 48 hours, and based on the results, the biocide usage is either increased or decreased. They are not specific to any single bacteria, so you are just checking for a general kill rate. Usually 1,000 to 10,000 total colony count is considered good control with 100,000 colony count considered as acceptable, but high. ATP testing is also used. This measures an enzyme present in all biological matter. By testing for the different levels of this enzyme in the water, you can determine in a few minutes if the biological growth in the system is being controlled by the biocide. Again, this is not specific to Legionella, and will only determine overall biological levels.Binax has a test that in 15 minutes will test specifically for serogroup type 1 of Legionella. The test costs 30 times the cost of the dipsticks and will not give a specific count. It will determine if the bacteria is present, and then if it is, if it is above 100 colonies. This test is new, and is the start of more sophisticated field testing.The most effective test to determine if Legionella is present is to send a sample to a certified testing lab. This, unfortunately, will take up to two weeks to get results. Sometimes this result is after the horse has left the barn, and is used more as documentation than as a tool for prevention.In any case, testing for Legionella specifically is very difficult. Normal augers used for other bacteria testing will not grow Legionella unless an iron-impregnated auger is used.

Incoming Water Disinfection

  1. The water coming to a facility from the potable water supplier can contain Legionella bacteria.
    1. Chlorine levels used in drinking water for disinfection of bacteria are not sufficient to kill Legionella bacteria in the water.
    2. Legionella can enter the cooling tower with the makeup water. In this case, the cooling water is constantly being infected.
    3. Legionella will enter the facility potable water system, and where the hot water is not kept over 133°F, the bacteria will thrive.
    4. Legionella bacteria, once in the potable water system, will propagate on the internals of the pipes where the pipes have become rough or some corrosion has occurred.
    5. Legionella will become an aerosol and infect people at showerheads, from humidification, and in any whirlpools or hot tubs in the facility.
    6. If Legionella is present in the potable water system, the entire system will have to be decontaminated via:
      1. Chlorination of the entire potable water system with a minimum of 50-ppm chlorine.
      2. Removal and replacement of the piping system
      3. Silver anode showerheads to deter the bacteria at the showerhead.
      4. Constant introduction of 0.1 to 0.5 ppm of chlorine dioxide into the bulk water system. This product is used in potable water systems where iron, manganese or trihalomethane is a problem, so it is accepted for use in potable water systems. It will effectively kill Legionella and can penetrate a biofilm.

Filtration of the Cooling Water System

  1. The lower the solids level in a cooling water system, the lower the potential for scale, corrosion, or biological growth, so filtration can keep a cleaner cooling tower system.
  2. Side stream filtration down to 20 micron will dramatically reduce the solids loading in the cooling tower. Size the unit for 5 – 10% of the system circulation
  3. Cyclonic filters will help remove solids. They only remove down to 70 micron, so some silt will still drop out in the system. Use these filters where you need to filter the entire system circulation, or where there is significant solids fouling due to high levels of solids in the intake air: construction, rubber production, farm areas, refineries, and locations near roads. In general, the prevention of Legionella in a facility requires maintaining a clean system. Filter the water, maintain sufficient biocide, maintain the correct biocide, and manually clean and disinfect the system twice a year.

Guardian’s Potable Water Treatment Solutions

1. Chlorine Dioxide
Legionella | Cooling Towers | Potable Water

2. Potable Water Disinfection – New Construction/Emergency

3. General Filtration

4. Remote Monitoring
eController | Guardian Reports | Data Management

To learn more about Guardian water treatment equipment and systems, talk to a Guardian specialist.

Request Contact800-297-8266

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