The Cooling Tower Water Chemistry Challenge

Cooling towers are the unsung heroes behind many industrial processes, quietly keeping things cool while fighting a battle against scaling, mineral buildup, and excessive water usage [2]. Proper water chemistry management is essential to protect assets, prevent microbial proliferation, and safeguard public health [1].

26%

Water savings with optimized treatment [2]

50%

Maintenance reduction [2]

4-6

Optimal cycles of concentration [4]

$28K

Annual savings from optimized cycles [6]

The Central Harlem Legionnaires' disease outbreak—which sickened over 100 individuals and claimed seven lives—traced back to contaminated cooling towers, underscoring the critical importance of effective water treatment and monitoring [1]. Balancing cycles of concentration, scale prevention, and environmental compliance requires a comprehensive approach integrating physical and chemical treatment methods.

Cooling Tower Water Chemistry Management 

Regulatory Reality

Under 40 CFR 423.16, cooling tower blowdown must meet strict discharge limits for priority pollutants, including total chromium below 0.2 mg/L and total zinc below 1.0 mg/L [5]. Additionally, 40 CFR Part 63 Subpart Q prohibits the use of chromium-based water treatment chemicals in industrial process cooling towers [8].

Understanding Cycles of Concentration

Cycles of concentration (COC) is a fundamental concept in cooling tower operation. When water evaporates in a cooling tower, only pure H₂O is driven off, leaving dissolved solids behind. The ratio of salt concentration in the tower to the amount found in the makeup water is referred to as cycles of concentration [6].

How Cycles Work

If three cups of boiling water were allowed to boil away to one cup, the residual cup would contain a three-fold concentration of soluble water salts. The water would be said to be at three cycles of concentration [4].

Makeup = Evaporation + Blowdown [7]

The Optimal Range

The savings effected by a recirculating system compared to a once-through system are maximized at about four to six cycles of concentration. Below this range, treatment costs become prohibitive. At high cycles (e.g., eight to 10), the additional water savings generally are not commensurate with the increased difficulty of effective treatment [4].

Water Savings Potential

Figure 1 in the ChemTreat guide shows that after six or seven cycles of concentration, the water savings potential is small compared to the increase in circulating water contaminant concentrations [7]. The sweet spot balances water conservation with manageable chemistry.

Why Scale is the Enemy of Efficiency

The Consequences of Scaling

  • Reduced heat transfer - Scale acts as insulation, reducing cooling efficiency
  • Increased energy costs - Systems work harder to maintain temperatures
  • Flow restrictions - Scale narrows pipes, causing pressure drops of 20-30 psi [2]
  • Equipment damage - Premature failure of heat exchangers and components
  • Increased maintenance - Costly outages for cleaning or repairs [6]

How Scale Forms

As cycles of concentration increase, dissolved minerals like calcium carbonate and magnesium silicate exceed their solubility thresholds and precipitate onto heat exchange surfaces [6].

Scale formation is accelerated by:

  • High hardness in makeup water
  • Elevated pH and alkalinity
  • High temperatures on heat transfer surfaces
  • Biofilm that provides attachment points [2]

Real Proof: GenGard Implementation at Canadian Steel Mill

FEATURED CASE STUDY

Facility: Integrated Steel Mill

Location: Canada

Application: Secondary non-contact cooling tower

The Challenge

The cooling tower required high acid and excessive blowdown to prevent deposition caused by calcium and phosphate. The plant was feeding acid to depress pH but still had to reduce cycles of concentration to only two. This mode of operation generated excessive blowdown and sent treatment chemicals to the drain [6].

The Solution & Results
  • GenGard technology implemented with stress-tolerant polymer and alkaline enhanced chemistry
  • Cycles increased from 2 to 4 without acid addition
  • 250 million liters of water saved annually (50% reduction)
  • Eliminated $5,000 annual acid cost
  • Total savings: $28,000 per year
  • Eliminated environment, health & safety risks associated with acid use
Read Full Case Study

"The increased cycles reduced the amount of water and chemicals being consumed. Total savings equate to $28,000 per year and eliminate the environment, health & safety risk associated with the use of acid."

- Veolia Water Technologies

[6]

Methods to Increase Cycles of Concentration

Makeup Water Softening

Ion-exchange softeners replace scale-forming calcium and magnesium ions with sodium. Soft water allows cooling towers to operate at higher cycles of concentration, resulting in less frequent blowdown [1].

Note: 100% softened water can be corrosive, so partial softening or blending is often employed [1][7].

Acid Feed

Acid feed for pH control can enhance corrosion inhibitor performance and control calcium carbonate scaling. Benefits include operating at lower alkaline pH, reducing corrosion inhibitor requirements, and increasing cycles [7].

Requires careful handling to prevent concrete basin damage [7].

Advanced Oxidation

Hydroxyl-based AOP generates powerful oxidizing agents that break down dissolved minerals, destroy biofilm, and prevent scale formation—allowing higher cycles without chemical additives [2].

NREL-validated 26% water savings, 50% maintenance reduction [2].

Side-Stream Filtration

Removes suspended solids by filtering 3-10% of recirculating water, resulting in better heat transfer, reduced maintenance, and improved chemical efficiency [1].

Cascading Towers

Pair of cooling towers placed in series—the second uses the first tower's blowdown as makeup, reducing overall water usage while treatment chemicals carry over [7].

Alternative Water Sources

Gray water, RO permeate, RO concentrate, or municipal wastewater can supplement or replace conventional makeup [7][10].

Environmental Compliance: Federal Regulations

40 CFR 423.16 - Pretreatment Standards [5]

Cooling tower blowdown discharged to POTW must meet:

PollutantMaximum (mg/L)
Chromium, total 0.2
Zinc, total 1.0
126 Priority Pollutants in added chemicals No detectable amount
40 CFR Part 63 Subpart Q - NESHAP [8]

No owner or operator of an IPCT shall use chromium-based water treatment chemicals in any affected cooling tower.

Compliance demonstrations:

  • Water sample analysis (hexavalent chromium ≤ 0.5 ppm) OR
  • Records of chemical purchases showing no chromium products

Effective: September 8, 1994 for existing towers [8]

ASHRAE Standard 188 Requirements

Facilities must maintain a Water Management Program with routine monitoring including makeup water (hardness, alkalinity, conductivity, pH), basin water (temperature, pH, conductivity, ORP), weekly dipslide testing for bacteria, and quarterly Legionella sampling [1].

Monitoring Strategies for Optimal Control

ParameterLocationFrequencyControl Limit
Total Hardness Makeup Water Routine Varies by system
Alkalinity Makeup Water Routine Varies by system
Conductivity/TDS Makeup & Basin Continuous/Routine Set by cycles target
pH Basin Water Continuous 6.8-7.2 (for orthophosphate) [7]
Temperature Basin Water Continuous Per design
ORP Basin Water Continuous 650-750 mV [1]
Total Bacteria Basin Water Weekly Dipslide testing [1]
Legionella Basin Water Quarterly minimum <1 CFU/mL [1]

Real Proof: NREL-Validated AOP Technology

THIRD-PARTY VALIDATION

Study: National Renewable Energy Laboratory (NREL)

Client: General Services Administration (GSA) / U.S. Department of Energy

Technology: Hydroxyl-Based AOP

Validation Results
  • 26% water savings (estimated 23-30%)
  • 50% maintenance reduction
  • Met GSA water standards without additional chemicals
  • 2-year payback based on GSA average water costs
Read Full Study

"Hydroxyl-Based AOP can push COC to higher levels, using less water, reducing blowdown, and limiting harsh chemicals—leading to a smaller environmental footprint."

- Clear Comfort

[2]

Alternative Water Sources for Sustainable Cooling

Gray Water

Benefits: Reduces demand for municipal water; cycled PO₄ serves as mild steel corrosion inhibitor [7]

Challenges: Increased phosphate fouling potential; microbial nutrient concerns [7]

RO Permeate

Benefits: Water largely devoid of ionic species; exceptionally high cycling possible [7]

Challenges: High unit water cost; more corrosive water requires higher inhibitor residuals [7]

RO Concentrate (Reject)

Benefits: Avoids wastewater discharge costs; reduces conventional makeup demand [7]

Challenges: May reduce attainable cycles; higher corrosion rates from chlorides/sulfates [7]

Condensate Recovery

Collecting condensation from air handlers provides high-quality makeup water with little treatment required—simple and cost-effective [10].

The Vulcan Advantage: Chemical-Free Scale Prevention

Vulcan's physical impulse technology addresses cooling tower scaling at its source—without chemicals, acid, or softening chemicals that create disposal challenges.

  • Prevents scale formation on all heat transfer surfaces
  • Destroys biofilm that anchors scale [2]
  • Zero chemical handling or storage
  • No discharge compliance issues
  • Zero maintenance, no consumables
  • External installation - no downtime

By eliminating scale, Vulcan allows cooling towers to operate at higher cycles of concentration safely—reducing blowdown, conserving water, and lowering chemical treatment costs while maintaining environmental compliance.

Compliance Ready

No chromium, no zinc, no priority pollutants—just clean, scale-free operation that meets 40 CFR 423.16 and Part 63 Subpart Q requirements.

Recommended Vulcan Models for Cooling Towers

Different cooling tower sizes require different models. Create an account for detailed specifications and pricing.

SMALL TOWER

Vulcan S100 / S150

Up to 500 tons

Individual cooling towers

Small industrial processes

Commercial HVAC

MEDIUM TOWER

Vulcan S250 / S350

500-2,000 tons

Industrial process cooling

Multiple tower systems

District cooling

LARGE TOWER

Vulcan X-PRO Series

2,000+ tons / multiple towers

Power plant cooling

Large industrial complexes

Central utility plants

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The ROI of Optimized Cooling Tower Chemistry

Annual Savings - 1,000 Ton Industrial Cooling Tower
Water savings (from increased cycles - 26% reduction) [2] $12,000 - $18,000
Chemical treatment reduction (acid, biocides, inhibitors) $8,000 - $15,000
Maintenance labor savings (50% reduction) [2] $5,000 - $10,000
Energy savings (improved heat transfer) $4,000 - $8,000
Extended equipment life (reduced scale corrosion) $3,000 - $6,000
Total Annual Savings $32,000 - $57,000
The Compliance Cost

One environmental violation for cooling tower discharge exceeding chromium or zinc limits can cost $50,000+ in fines plus mandated system upgrades. Chemical-free scale prevention eliminates this risk entirely.

Get Exact Pricing for Your Cooling Tower

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Account registration takes less than 2 minutes.

References

  1. RL Deppmann. (2025). 5 Effective Cooling Tower Treatment and Monitoring Strategies.
  2. Clear Comfort. (2024). Supercharge Your Cooling Towers with AOP: Higher Cycles of Concentration & Less Scaling.
  3. Veolia Water Technologies. GenGard Improves Cooling Tower Efficiency & Reduces Operating Costs at a Steel Mill.
  4. Materials Performance Magazine. (2025). Open Recirculated Cooling Water Systems.
  5. 40 CFR 423.16 – Pretreatment standards for existing sources (PSES).
  6. ChemTreat. (2022). Three Practices for Sustainable Cooling.
  7. 40 CFR Part 63 Subpart Q – National Emission Standards for Hazardous Air Pollutants for Industrial Process Cooling Towers.
  8. Los Angeles Department of Water and Power. (2023). Cooling Towers: Saving Water Saves Money.

Cooling Tower Water Management Checklist
  • Establish water management team per ASHRAE 188
  • Document current cycles of concentration and target range
  • Verify no chromium-based treatment chemicals are used [8]
  • Monitor blowdown for compliance with 40 CFR 423.16 limits [5]
  • Implement scale prevention to maintain heat transfer efficiency
  • Conduct weekly dipslide testing for total bacteria [1]
  • Perform quarterly Legionella sampling [1]
  • Document all monitoring and corrective actions

With Vulcan, scale prevention is documented and verified—one less variable in your compliance program.

Optimize Your Cooling Tower Chemistry

Balance cycles of concentration, prevent scale, and meet environmental compliance—all without chemicals or discharge concerns.

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About the Author

Waslix (Vulcan Mineral Descaler) provides non-chemical, maintenance-free scale prevention for cooling towers worldwide. Our technology helps industrial facilities optimize cycles of concentration, reduce blowdown, and meet environmental compliance without hazardous chemicals. Create an account for detailed model specifications and pricing.