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State of California Department of Pesticide Regulation - page 70 / 104





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the useful life of the equipment. Effective water treatment requires monitoring water quality and taking corrective action before undesirable conditions occur. It is much more difficult and expensive to correct buildups of scale deposits, slimes, fungi, algae, and bacteria than it is to prevent or retard their development. Facility managers must consider all factors that endanger public health or interfere with the efficient operation of a cooling system. They must plan control measures accordingly since one problem, such as scale buildup, may promote another problem, such as bacteria buildup.

The maintenance of water quality and prevention of microorganism buildup requires testing equipment that measures levels of antimicrobial compounds to assure that adequate concentrations are present for effective control. One method of doing this is by applying intermittent doses. This involves adding sizeable doses of chemicals to the water periodically to bring the concentration of antimicrobial pesticide to a lethal level and then maintaining this level for a prescribed period. Another method involves adding lower levels of pesticides continuously to maintain a suitable concentration at all times to suppress the microorganisms. In once-through systems, intermittent doses are used to reduce the waste of antimicrobial chemicals.

Methods of Application

Antimicrobials are applied either by pouring measured doses into the cooling water or by using automatic feeding equipment. Automatic feeding equipment requires routine maintenance and proper calibration. No matter how the antimicrobial pesticide is applied, periodically test the cooling water to verify the antimicrobial concentration and to monitor levels of harmful organisms.


The use of antimicrobial pesticides in water cooling systems has several associated hazards. In concentrated form, antimicrobials may cause serious injury if they are spilled on the skin or splashed into the eyes. Some are highly corrosive and may damage equipment or surfaces if a spill takes place. Most of these chemicals are harmful to wildlife and may cause environmental problems if an accidental or improper discharge occurs.

Always read the label on the antimicrobial container to become familiar with hazards to people and the environment. Wear all protective equipment required by the label while handling, mixing, or applying the material and while servicing, adjusting, or repairing automatic feeding equipment.

Keep pesticide containers in a locked area that is dry and well-ventilated. If automatic feeding equipment is used, be sure this is also enclosed in a locked area.

Apply antimicrobials according to the dosage prescribed on the label. Avoid over-application since high concentrations in the water system may injure people and could damage the cooling equipment. Over-application is also in conflict with label use directions and is therefore illegal.

Antimicrobial pesticides in the discharge water from a blowdown operation may cause illegal contamination of the environment if the water flows into municipal drains, streams, rivers, or enters the groundwater. Avoid environmental contamination by discharging blowdown water into approved holding containers and/or transporting it to an approved disposal site. Check with the local agricultural commissioner for disposal information and requirements.


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