WTS | First Defense utilizes procedures from both OSHA Section III Chapter 7, ASHRAE Standard 188, and ASHRAE guideline 12-2000 for minimizing the risk of Legionellosis associated with building water systems.  Inspections are utilized to confirm systems are clean to eliminate the source of nutrients for Legionella and other forms of bacteria. Distribution trays along with cold water basins are periodically checked for debris or other visible signs of fouling.

Recommendations will be made for providing additional means of debris control such as side stream filters, strainers, water source, and bag filters.  In addition, the current water treatment program will be evaluated to ensure it is functioning properly.  This will minimize microbiological, scale, and corrosion by-products which are additional risk factors.

See what’s included in our Assessment

WTS | First Defense utilities on line eMaint CMMS software for work orders.   All work orders for service will generate a Service Report.  All data will be maintained and easily tracked for trends and historical data.  Service Report data is shared with customers.


Cleaning and Disinfection Procedures

  1. Contact your water treatment service provider to make sure that they are using the correct water treatment chemicals to treat your cooling tower.
  2. A typical cooling tower water treatment program should consist of an oxidizing biocide, a non-oxidizing biocide and a corrosion inhibitor.
  3. Chemicals need to be adjusted based on temperature and water usage.
  4. If you suspect your cooling tower is dirty, contact a professional cooling tower cleaning company to conduct and assessment.
  5. Have your tower professional cleaned and disinfected if it is called for.
  6. OSHA recommends cooling towers be cleaned at least twice per year.
  7. Have your cooling towers periodically tested for Legionella.

The three [3] distinct areas of our 360 Degree Legionella Management Service are:

  1. Legionella Risk Assessment & Management Plan
  2. Water Treatment Services for Legionella Prevention
  3. Legionella Emergency Outbreak Response Team

Our Procedures

Our procedures comply with all state requirements for cooling tower disinfection and in general goes above and beyond.


Disinfection definitions

  • Online disinfection means – Dose the cooling tower water system with either a different biocide or similar biocide at an increased concentration than currently used.


  • Online decontamination means – Dose the recirculation water with a chlorine-based compound equivalent to at least 5 mg/l (ppm) free residual chlorine for at least one hour; pH 7.0 to 7.6.


  • System decontamination means – Maintain 5 to 10 mg/l (ppm) for a minimum of one hour; drain and flush with disinfected water; clean wetted surface; refill and dose to at 1-5 mg/l (ppm) of free residual chlorine at pH 7.0 to 7.6 and circulate for 30 minutes. Refill, re-establish treatment and retest for verification of treatment.


There are many factors in determining the most effective sanitization protocol for a given cooling system.  Establishing a single protocol for every situation would not be practical. These guidelines merely provide a minimum expectation of what should be done, but industry experience and system knowledge will allow the water treatment expert to prescribe the most effective solution.  That is why certified, licensed, and experienced water treatment professionals should be used.


WTS | First Defense usually recommends at least an “online decontamination” as opposed to the less stringent “online disinfection” to increase the potential for success, especially if we are called in to a facility that we do not administer the water treatment program.  The money potentially saved with the lesser of the two procedures quickly vanishes if the protocol is unsuccessful and must be repeated or ramped up to the next level.  Since chlorine is such a volatile oxidizer, it is usually the biocide of choice for a fast sanitization of a cooling tower.


The key concepts to remember in minimizing the potential risk of Legionella growth and proliferation are:

  • Maintain consistent water treatment program
  • Ensure good solids/bleed control
  • Employ two different biocides, oxidizer and non-oxidizer
  • Clean cooling towers at least twice per year

A basic cooling tower cleaning procedure is detailed below.  This is what New York State defines as a “system decontamination”. This, or a comparable procedure, will be part of the water treatment program.


  1. Sodium hypochlorite and bio-dispersant are added to system and circulated for at least one [1] hour [longer duration is better. Free Chlorine Residual is checked during this circulation to insure the proper level is present for disinfection.
  2. Each cell will be power washed from top to bottom.
  3. Power washing will be completed at each tower and vacuumed clean removing all debris and foulants.
  4. Next, the system will be filled with fresh city water.
  5. Repeat this process as required.
  6. Additional sodium hypochlorite and bio-dispersant are added to system and circulated for continuous protection.
  7. Next a tower system valve should be cracked open to help reduce the chlorine residuals.
  8. The tower is now ready for a continuous chemical treatment program.

There are other adjustments or additions that we implement as needed, including a 24-hour pre-cleaning, where bio-dispersant and an oxidizing biocide are added a day or two before the mechanical cleaning.  Another is the polishing of the system after the cleaning with additional biocide.  In any event, the maintenance program needs to recommence immediately after the sanitization is complete.