Cooling Tower Discharge: The Basics of Bleeding Cooling Towers and EPA – NPDES Regulation

What is the Purpose of Bleeding Cooling Towers?

The controlled discharge from cooling towers and other recirculating water systems is designed to maintain a certain level of water use efficiency or cycles of concentration.  Evaporation causes the concentration of naturally occurring dissolved solids in cooling tower water to be greater than the water source from which it started.  The scrubbing effect water has on air pulled through the cooling tower to increase evaporation causes common, naturally occurring bacteria to become more concentrated in cooling tower water.  The safest and most environmentally-responsible way to get rid of the controlled discharge of cooling tower water is to drain it to the sanitary sewer.

Unfortunately, many older and rural systems were designed to drain cooling tower water directly to drainage tile fields, collection ponds, ditches, creeks or other storm sewers.  In an effort to protect the environment, the Environmental Protection Agency (EPA) enacted The Clean Water Act in 1987.  The intention is to restrict and eventually eliminate the discharge of “pollutants” to storm sewers and other surface water sources.

The most acceptable means of discharging (i.e. bleeding) water from a cooling tower is to a sanitary sewer and on to a sewage treatment facility.  So, what if there is no sewage treatment facility available?  Under certain circumstances, a permit under a process called National Pollution Discharge Elimination System, or NPDES is required.

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How Does the NPDES Process Work?

There are several factors considered in the NPDES permit approval.  Most permits are issued on a case-by-case basis.  Factors in the approval process include:  location of the cooling tower, availability of sewage treatment, discharge water flow or volume, discharge temperature, receiving waterbody temperature, discharge pH, residual chlorine, other pollutants, waterbody location and seasonal/natural variation, the monitoring plan etc.

As a resource for the application process, we highly recommend further information be obtained directly from the EPA at

For more information about our cooling tower services at Chardon Labs, as well as best practices in managing your water systems, please contact our Technical Support staff at 888-486-9263 or fill out our online contact form. We are always available to answer your questions and provide our expert recommendations!

matt welsh
Matt Welsh
Vice President, Water Consultant at | Website | + posts

Matt Welsh is the Vice President and Water Consultant at Chardon Labs.  He helps consult a wide range of customers utilizing various methods of water treatment, from chemical to chemical-free approaches, large and small applications, and across a wide range of geographical influences.  With 20 years of water treatment experience, including a wide range of troubleshooting and service in potable water and non-potable HVAC and industrial applications, he is an expert in water treatment chemistry for cooling towers, boilers, and closed-loop systems.