Water Treatment.
24 RCNY § 8-05
in effect§ 8-05 Water Treatment.
Prior to changing an existing chemical treatment system or introducing a new chemical treatment agent, cooling tower design, installation, operation, and maintenance must be evaluated by a qualified person to ensure compatibility between the chemicals and the cooling tower system's materials, and to minimize microbial growth and the release of aerosols. The evaluation must describe the optimum level of chemicals to achieve the desired result in a manner which can be used as a system performance measure. All records required pursuant to this section must be retained and produced in accordance with subdivision (a) of 24 RCNY § 8-07.
(a) Daily automatic treatment while in operation. Water in a cooling tower system must be treated at least once a day when the system is in operation and such treatment must be automated, unless the maintenance program and plan explicitly states how manual or less frequent biocide additions will provide effective control of Legionella growth.
(b) Recirculating system. A cooling tower system must continually recirculate the water when it is in operation. Any period of no circulation lasting three (3) days or more in any part of the cooling tower system requires that applicable risk management procedures described in the maintenance program and plan be carried out and documented to achieve effective biofilm and microorganism control.
(c) Chemicals and biocides. Chemicals and biocides must be used in quantities and combinations sufficient to control the presence of Legionella, minimize biofilms, and prevent scaling and corrosion that may facilitate microbial growth. Only New York State Department of Environmental Conservation approved oxidizing chemicals may be used as the primary biocide control. For systems where oxidizing chemicals cannot be used as the primary biocide to control the presence of Legionella building owners must submit an alternative plan for effective bacteriological control for approval by the Department.
(1) Biocide applications. Any person who performs cleaning and disinfection or applies biocides in a cooling tower system must be a commercial pesticide applicator or a pesticide technician certified in accordance with the requirements of Article 33 of the New York State Environmental Conservation Law and 6 NYCRR Part 325, or a pesticide apprentice under the supervision of a certified applicator.
(2) Registered biocides. Only biocide products registered with the New York State Department of Environmental Conservation may be used to meet the disinfection requirements of this Chapter.
(3) Records. Water treatment records must be kept for all chemicals and biocides added, noting the purpose of their use, the manufacturer's name, the brand name, the safety data sheet, the date and time of each addition, and the amount added each week.
(4) Chemical and biocide additions. Chemicals and biocides must be added in accordance with this section and the procedures described in the maintenance program and plan addressing, as applicable, feeding mechanism, feeding location, frequency, set timer, duration, triggering events, control procedures, and target biocide residuals. Water treatment chemicals and biocides must be used in accordance with the product label and manufacturer's instructions.
(d) Non-chemical water treatment devices restricted. Only biocide products registered with the New York State Department of Environmental Conservation may be used to meet the disinfection requirements of this Chapter. Non-chemical water treatment devices that employ alternative technologies to control biological growth may not be used in lieu of chemical biocide unless approved by the Department. Nonchemical water treatment devices may be installed as part of a cooling tower system as specified in the management program and plan, provided that the required chemical water treatment also being used adequately controls for Legionella.
(e) Fill / makeup water. Fill water for commissioning or startup of a cooling tower system must be obtained from a municipal water supply. For makeup water, owners may use municipal water or water derived from a nonpotable water source. If water from a nonpotable water source is used, the owner must submit an alternative water source plan. This plan is a separate document in addition to the maintenance program and plan required by 24 RCNY § 8-03 and must be approved by the Department. The alternative water source plan must identify each nonpotable water source and include provisions for adequate design of the treatment and control components and on-going evaluation to eliminate any risk to public health.
(f) Water quality monitoring.
(1) Frequency. Water quality parameters, including but not limited to pH, temperature, conductivity and biocidal indicators, must be measured and recorded as specified in the management program and plan as follows:
(A) Manual measurements. At least three times each week, provided that no more than two days pass without such measurement when the cooling tower system is operating.
(B) Continuous, automated and/or remote measurements. When continuous, automated and/or remote measurements and recordings are used, the management program and plan must show how effective measurements of system process controls are being monitored.
(2) Minimum weekly biological process control indicators. A bacteriological indicator to estimate microbial content of recirculating water must be collected and interpreted in accordance with Table 8-2 at least once each week while the cooling tower system is operating. Indicators must be taken at times and from water sampling points, as detailed in the maintenance program and plan, that will be representative of water microbial content. Indicators may be taken at any time from constant chemical treatment systems. Indicators from systems that use intermittent biocide applications must be taken before biocide application and reflect normal cooling tower operating conditions. If indicator is performed by HPC, it must be analyzed by a laboratory accredited by the New York State Environmental Laboratory Approval Program (ELAP).
(3) Legionella samples. Legionella culture testing must be conducted at least as frequently as every month, with no more than 31 days between sample events, during cooling tower system operation. A Legionella sample must be analyzed by a laboratory accredited by the New York State Environmental Laboratory Approval Program (ELAP). The results of such a test must be recorded in a final analytical report from the laboratory that includes a copy of the signed chain of custody and the laboratory’s ELAP certification number. Test results of all Legionella species at or above the magnitude of level 4 as indicated in Table 8-1 must be reported to the Department within 24 hours of receiving the test results. Test results of all Legionella species must be evaluated by the qualified persons and the management and maintenance team to ensure Legionella control. Additional emergency Legionella sampling must be conducted if any of the following occur:
(A) Power failure of sufficient duration to allow for growth of bacteria;
(B) Loss of biocide treatment sufficient to allow for growth of bacteria;
(C) Failure of conductivity controls to maintain proper cycles of concentration;
(D) At the request of the Department upon a determination that one or more cases of legionellosis is or may be associated with the cooling tower, based on epidemiological data or laboratory testing; or
(E) Any other conditions specified by the Department.
(4) Monitoring and sampling locations. System monitoring and sampling locations must be representative of the entire cooling tower system. The system must be operating with water circulating in the system for at least one hour prior to water quality measurements or collection of samples.
(5) Water quality corrective actions. The maintenance program and plan must identify the procedures, responsible parties, required response time(s) and notification protocol for corrective actions and must include, at a minimum, corrective actions that must be implemented according to the result levels in Table 8-1 and Table 8-2. For hyperhalogenating, as indicated in Table 8-1, dose the cooling tower water system with 5 to 10 ppm Free Halogen Residual for at least 1 hour. The hyperhalogenation must be carried out with the appropriate pH level for effective disinfection. The disinfectant and pH level must be documented in the corrective action procedures.
Table 8-1. Corrective actions required for Legionella culture results.
Level Legionella Culture Result Process Triggered by Legionella Culture Results
1 <10 CFU/ml If not detected, maintain water chemistry and biocide levels. If Legionella is detected but <10 CFU/ml, review water treatment program and adjust water chemistry and biocide levels, if needed.
2 ≥10 CFU/ml to <100 CFU/ml Initiate disinfection by increasing biocide concentration or using a different biocide within 24 hours; review treatment program; and retest water within 3 - 7 days. Subsequent test results must be interpreted in accordance with this Table until level 1 is reached.
3 ≥ 100 CFU/ml to <1,000 CFU/ml Initiate disinfection by increasing biocide concentration or using a different biocide within 24 hours, reviewing treatment program, performing visual inspection to evaluate need to perform cleaning and further disinfection. Retest water within 3 - 7 days. Subsequent test results must be interpreted in accordance with this Table until level 1 is reached.
4 ≥ 1,000 CFU/ml Initiate disinfection by increasing biocides within 24 hours. Within 48 hours perform full remediation of the tower by hyperhalogenating, draining, cleaning, and flushing. Review treatment program, retest water within 3 - 7 days. Subsequent test results must be interpreted in accordance with this Table until level 1 is reached. For Legionella results at this level, notify Department within 24 hours of receiving test results.
Table 8-2. Corrective actions required for bacteriological indicator results.
Level Heterotrophic Plate Count and Dip Slide Result Process Triggered by Test Results
1 <10,000 CFU/ml Maintain water chemistry and biocide levels.
2 ≥10,000 CFU/ml The management and maintenance team must initiate monitoring of disinfectant residual three times per day until water treatment achieves target biocide residuals for a minimum of 24 hours. If this is not achieved within three days, collect a Legionella sample and continue to adjust water treatment program. Conduct a quality control review of the water treatment program and make modifications to dosing, chemicals and biocides, bleed off or other process controls to achieve bacteriological control. Retest water for bacteriological indicators 48 hours after achieving target biocide residual. Subsequent test results must be interpreted in accordance with this Table until level 1 is reached.
(Added City Record 4/7/2016, eff. 5/7/2016; amended City Record 4/8/2026, eff. 5/8/2026)
Source: City of New York, Charter, Administrative Code and Rules (American Legal Publishing XML export, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/newyorkcity/latest/NYCrules/0-0-0-97833Fetched: 10/24/2026