A growing body of case studies shows utilities cutting makeup water 20–30% by running cooling towers at the highest possible cycles of concentration and by using treated municipal wastewater as makeup, with multi‑year paybacks to match.
Thermal power plants are among the biggest water users on the planet. In Europe, industry withdrawals account for ~45% of all abstracted water, and more than 80% of that goes to cooling (climate-adapt.eea.europa.eu). The way a plant cools matters: once‑through systems (river or ocean water passed once through condensers) withdraw colossal volumes (~76,000–190,000 L/MWh), while recirculating evaporative towers cut withdrawals to ~1,900–4,500 L/MWh by losing water mainly to evaporation and drift (same source; MWh = megawatt‑hour) (climate-adapt.eea.europa.eu).
Modern recirculating towers typically consume only 0.3–0.6 gallons (1.1–2.3 L) per kWh generated, compared with 20–50 gal/kWh for once‑through systems (researchgate.net). In Indonesia, where coal plants still dominate, cooling needs remain massive: coal‑fired plants consume on the order of 222 million m³ per year, with policymakers projecting that 10% of the population will face a “water crisis” by 2045 (ije-pyc.org) (ije-pyc.org).
Cooling tower water math
Two strategies dominate utilities’ current water‑saving playbook: push cycles of concentration (CoC) higher without scaling, and swap freshwater for alternative sources, most notably municipal reclaimed water. CoC (the ratio of dissolved solids in recirculating water to makeup water) is the master lever: higher CoC linearly reduces both makeup and blowdown flows. As a rule of thumb, raising CoC from 3 to 6 roughly halves blowdown flow. One published figure shows that at 3× CoC blowdown could be ~600 gpm, while at 6× it may drop to ~250 gpm for a fixed load (gpm = gallons per minute) (power-eng.com).
Case studies back up the math. Increasing CoC from 6.5 to 9 (∼38% rise) saved ~1.1×10^6 m³ of fresh water per year in a modeled plant (researchgate.net). A Chinese site that installed a crystallization‑based softening system lifted CoC from 4.5 to >9, cutting makeup (and wastewater) by 150 m³/hr and saving about $200,000 annually (mdpi.com). And a Saudi Aramco pilot switched to higher‑quality makeup and doubled down on CoC, moving from 2 to 3.5 and trimming cooling water demand by 27% — ≈16,500 m³/year for a 1200‑ton chiller (watertechonline.com).
Scaling control and CoC limits
Operating at high CoC requires tight control of scale‑forming ions. As minerals concentrate, scale risk rises; for example, traditional phosphate inhibitors can hydrolyze at high CoC and precipitate calcium phosphate scale (researchgate.net). Operators track the Langelier Saturation Index (LSI, an index indicating calcium carbonate saturation tendency) and keep it near zero to avoid CaCO₃ deposition.
Plants use tactics from pretreatment to chemistry. Lime softening or circulating pellet fluidized beds (CPFBs) can remove hardness before the tower; one CPFB study crystallized calcium into grains and removed >60–90% of Ca²⁺, enabling the large CoC jump noted above (mdpi.com). Where acid is appropriate, dosing sulfuric acid or CO₂ converts bicarbonate to more soluble sulfate, and organic dispersants/polymer inhibitors curb precipitation (nepis.epa.gov). For hardness removal within a conventional program, many facilities integrate a softener upstream of the cooling loop.
Accurate chemical control matters as CoC rises. Plants commonly deploy a dosing pump for acid and pH control, then supplement with scale inhibitors as cycles climb. Dispersant polymers used in fouling control align with dispersant chemicals programs for towers.
Toward near‑zero blowdown
With treatment upgrades, CoC ≈8–10 — or even >12 in the literature — is now achievable, whereas older designs lived at 3–5 (mdpi.com) (researchgate.net). In water‑stressed regions, designs push toward near‑zero blowdown (ZLD, or zero liquid discharge), effectively maximizing CoC within scaling thresholds (power-eng.com) (watertechonline.com).
One path is to treat and reuse cooling tower blowdown. A Chilean power plant ran its blowdown through a single‑stage RO and crystallizer, achieving 96% reuse and feeding the permeate back as makeup — effectively decoupling the tower from potable supply; at 96% recovery, CoC can in principle rise arbitrarily because only ~4% net loss needs makeup (watertechonline.com) (watertechonline.com). Plants taking this route typically specify brackish-water RO for high‑TDS blowdown and integrate skids using standardized membrane systems.
Municipal effluent as makeup
Using treated municipal wastewater (often called TSE, or treated sewage effluent) for cooling tower makeup is gaining traction. Sector reviews note that many facilities are turning to municipal reclaimed water to reduce freshwater withdrawals (researchgate.net) (researchgate.net). Advantages include freeing potable water for other uses and reducing wastewater discharge.
In a Saudi oil/utility complex, secondary effluent with TDS ~1500 mg/L (TDS = total dissolved solids) and an LSI near 0 was treated and used as cooling makeup; condenser surfaces stayed clean, CoC rose safely to ~3.5 (versus only 2 on hard well water), and water use fell 27% (~16,500 m³/year for a 1200‑ton chiller) (watertechonline.com) (watertechonline.com). During the 8‑month trial, microbiological testing found no Legionella or enteric pathogens in the disinfected loop (watertechonline.com).
Technical reviews recommend tertiary‑level treatment and strong biocide control if using reclaimed effluent in towers (researchgate.net) (watertechonline.com). As a polishing step, many plants specify ultrafiltration before membranes, and reclaimed streams are often finished with RO (researchgate.net). Biocide programs built for higher organic loading map to packaged biocides used in cooling water treatment. One industry assessment even notes that treated wastewater “is often chemically superior to the fresh source, allowing increased cycles and decreased chemical costs” (prochemtech.com).
Economics and measured outcomes
The benefits of higher CoC and alternative makeup stack up: reduced freshwater intake, lower wastewater discharge, smaller effluent‑treatment loads, and in some cases energy savings. In the Saudi trial, using TSE and operating at higher CoC saved ~82,505 kWh/year (kWh = kilowatt‑hour) of power (watertechonline.com) and ~16,500 m³/year of water on ~1200 ton capacity; at $0.1/kWh and $1/m³, that suggests ~$25,000/year savings (rough guidance) on a modest installation (same source). In China’s CPFB case, the plant reported ~$200,000 annual savings from water and chemical reductions, with pretreatment operating costs of only $0.074/m³ (mdpi.com) (mdpi.com).
An Indonesian techno‑economic analysis that coupled RO with waste‑heat recovery estimated a payback ~4.9 years (ije-pyc.org). More broadly, a Texas study put the marginal cost of water savings from retrofitting once‑through to wet recirculating at just ~$0.00008 per gallon withdrawn, while converting to air‑cooled (dry) ran far higher at ~$0.0068–1.78 per gallon, depending on plant type (iopscience.iop.org) (iopscience.iop.org). A 2024 review found that treating and reusing blowdown yields ~13% additional water savings at lower implementation and operating cost than upgrading all makeup to demineralized quality for CoC>3 systems (sciencedirect.com).
Costs vary with local prices and plant specifics — capital for filtration/RO/softening, chemical programs (biocides/inhibitors), and piping are the main drivers — but benefits accrue continuously with operation. As a simple normalization, a plant saving 10,000 m³/yr at $0.5/m³ sees $5,000/year in direct water cost savings, excluding sewer/effluent fee relief. Many projects report 3–7 year paybacks when accounting for water, energy, chemical, and regulatory savings (ije-pyc.org) (mdpi.com).
What recent data show
Fourth quarter 2024 surveys indicate many plants are raising CoC from 3 to ~6–9 with state‑of‑the‑art treatment while bringing in alternative makeup; reported savings include 20–30% reductions in makeup flow (watertechonline.com) (mdpi.com). Annual water savings commonly fall in the 10^4–10^6 m³ per plant range, with energy savings of 10^4–10^5 kWh reported across pilots and case studies (researchgate.net) (watertechonline.com).
Crucially, where aggressive disinfection and monitoring are implemented, pilots report no enteric pathogens or Legionella in the loop (watertechonline.com). Across the literature, the technical feasibility and ROI of these measures are consistently attractive in water‑stressed contexts (watertechonline.com) (ije-pyc.org) (mdpi.com).
Source references
European Environment Agency (EEA), “Reducing water consumption for cooling of thermal generation plants,” EEA Climate‑Adapt (EU adaptation platform), 2015 (climate-adapt.eea.europa.eu). F. I. Jutail et al., “Use of treated sewage effluent as cooling tower makeup water – A pilot study,” Water Technology, Dec. 15, 2020 (watertechonline.com) (watertechonline.com). S. I. Müller et al., “Comparison of cooling tower blowdown and enhanced make up water treatment to minimize cooling water footprint,” J. Environmental Management, vol. 367, 121949, 2024 (sciencedirect.com). K. Rahmani et al., “Reducing water consumption by increasing the cycles of concentration…in a cooling system,” Applied Thermal Engineering, vol. 114, pp. 1363–1371, 2017 (researchgate.net) (researchgate.net).
R. Hu et al., “Application of chemical crystallization circulating pellet fluidized beds for softening and saving circulating water in thermal power plants,” Int. J. Environ. Res. Public Health, vol. 16(22), article 4576, 2019 (mdpi.com). V. A. Brilian et al., “Integrated wastewater and waste heat recovery system in coal‑fired power plants using reverse osmosis…,” Indonesian Journal of Energy, vol. 5(2), pp. 135–146, 2020 (ije-pyc.org) (ije-pyc.org). A. Loew et al., “Marginal costs of water savings from cooling system retrofits: a case study for Texas power plants,” Environ. Research Lett., vol. 11(10), 104004, 2016 (iopscience.iop.org). R. Zaken Porat, “Case study: 96% recovery of power plant’s cooling tower blowdown with an advanced reverse osmosis demonstration plant,” Water Technology, Aug. 28, 2023 (watertechonline.com) (watertechonline.com). J. A. Veil, “Use of reclaimed water for power plant cooling,” DOE/NETL Technical Report (Argonne Nat’l Lab), 2007 (researchgate.net) (researchgate.net).
