Cooling towers are often the single largest freshwater user in power plants — and the fastest water cut is to run them at higher cycles and tap treated wastewater. Recent field data show double‑digit water savings, fewer chemicals, and paybacks in months, with detailed cases from Saudi Arabia to Bali.
In industry, roughly 45% of all water withdrawals are by energy conversion, and of that over 80% is used for cooling processes (www.sciencedirect.com). Typical recirculating cooling towers consume 3–4 L of makeup water per kWh of electricity produced (world-nuclear.org).
Do the math: a 500 MW plant running at ~90% load (~10,800 MWh/day) might withdraw 32–44 million L/day for cooling, with several million L/day lost as blowdown. From a water-efficiency standpoint, the single biggest lever is to maximize cycles of concentration (COC — the ratio of dissolved solids in the circulating water to that in fresh makeup), a core recommendation in DOE Best Management Practice #10 (energy.gov).
Cycles of concentration and blowdown control
Increasing COC cuts blowdown and therefore makeup. Raising COC from ~2 to 4 cuts blowdown in half; from ~2 to 10 cuts it by ~87% (www.prochemtech.com). A DOE guide frames COC as “a key parameter” in tower management (energy.gov).
In practice, most systems run at only 3–4×C, but with well-managed chemistry many can safely reach 6–8×C (icsthailand.co.th). Advanced programs — for example, cation softening plus tailored inhibitors — report stable operation at COC ≈10 (www.prochemtech.com). Where makeup hardness is the constraint, plants commonly add a water softener to unlock higher cycles.
A documented industrial case increased COC from 2.2 to 10 (enabled by softened makeup), cutting annual blowdown from 8.08×10^6 to 1.08×10^6 gallons (30.6→4.08×10^6 L) and reducing makeup from 17.77×10^6 to 10.77×10^6 gallons — a ~26,500 m^3/year drop (∼39% saving) (www.prochemtech.com). Tailored antiscalants (chemicals that prevent mineral deposition) are commonly used; many programs pair them with a scale inhibitor formulated for the site’s water chemistry.
The same case’s hard-water program (COC≈2.2) needed 6,739 lb/yr of organic scale inhibitor ($24.9 k) (www.prochemtech.com). Switching to softened makeup (COC≈10) required only 3,370 lb/yr ($11.5 k) plus salt ($29.2 k) and produced 1.00×10^6 gal/yr of regeneration wastewater (www.prochemtech.com). Overall, total annual cost fell 32% ($246.5 k→$167.6 k) while saving 6.998×10^6 gal (26,500 m^3) of water (www.prochemtech.com).
In that example, an appropriately sized softener system (41 gpm) cost about $26k installed and paid for itself in ~4 months (www.prochemtech.com). Plants refining hardness with membrane pretreatment sometimes opt for nano‑filtration to remove calcium and magnesium at lower pressure than RO.
Operational monitoring and scaling risk
Scaling risk rises as COC increases, so control is essential. Modern programs monitor conductivity or Langelier Saturation Index (LSI — a qualitative indicator of scaling tendency) in real time and add antiscalants or adjust pH as needed (energy.gov) (www.prochemtech.com). Chemical feed is typically automated with a dosing pump matched to tower circulation rates.
Automated conductivity controllers can trim blowdown 40–60% (icsthailand.co.th). For chemistry programs, utilities often standardize a cooling tower chemical suite that includes dispersants, inhibitors, and biocides.
Alternative makeup: treated sewage effluent (TSE)
Plants looking to stretch freshwater supplies increasingly consider non‑traditional makeup, especially high‑quality treated municipal wastewater. Concerns (biofouling, organics, chloride) can be managed by pretreatment and rigorous biocide programs (watertechonline.com) (watertechonline.com). Pretreatment commonly includes membranes; many sites deploy ultrafiltration upstream of disinfection to remove suspended solids.
In a Saudi Aramco pilot, tertiary TSE (filtered and disinfected) fed continuously to a 1,200 ton–capacity cooling tower (ton is a cooling capacity unit). Over 8 months, microbiological sampling found no Legionella, coliforms or enteric viruses in the recirculating water (watertechonline.com). Disinfection with chlorine and isothiazolone was effective; several plants also add UV disinfection for low‑cost pathogen control.
Because the TSE had lower calcium and alkalinity than local groundwater, scale potential was minimal, enabling higher cycles. Groundwater makeup (TDS≈3,040 mg/L, COC=2 max) had produced visible scale on condensers (watertechonline.com). By switching to TSE — with lower hardness/TDS (1,500 mg/L) and LSI around 0–0.5 — the plant safely doubled its COC to ~3.5 (watertechonline.com), and no visible scale deposits were reported under the higher‑cycle TSE regime (watertechonline.com).
Industrial‑scale reuse is not new: Singapore’s NEWater program routinely supplies high‑grade recycled wastewater to power and industrial cooling, repurposing ~100% of sewage via its deep‑tunnel system; the Changi plant returns 59% of its effluent to industry (blended or raw) and the rest for indirect potable reuse (mdpi.com). For biocidal control on reclaimed sources, operators often standardize dedicated biocides to prevent biofilm formation.
Closing the loop: blowdown reuse and membranes
Another strategy is blowdown reuse: treating the tower’s own discharge for recycle. When towers are already at high COC (>3–4), processing blowdown by ultrafiltration/reverse osmosis (UF/RO) and reusing it can cut fresh intake by ~13% (www.sciencedirect.com). Plants pursuing this route typically integrate modular membrane systems sized to the blowdown flow.
Other alternatives include partially treated industrial wastewater or brackish water (with robust treatment). A Spanish brewery, for instance, split its wash‑water between cooling and pre‑wash after activated‑carbon detoxification (researchgate.net). For higher TDS feeds, power plants commonly turn to brackish‑water RO to deliver consistent makeup quality.
Disinfection options on reclaimed or saline sources vary by site; some plants adopt on‑site chlorine generation via electrochlorination to avoid gas‑storage hazards.
Cost and policy signals
Losses from blowdown can be sizeable: a 1000 MW wet‑cooled plant (~4 L/kWh) uses ~4×10^6 m^3/yr (world-nuclear.org). Raising COC from 3→6 would roughly halve blowdown, saving ~1–2×10^6 m^3/yr on such a plant. At Indonesian utility rates (~IDR 9,000–18,000 per m^3, ~$0.59–1.21/m^3) each 10^6 m^3 saved is worth $0.6–1.2 M/yr (mdpi.com).
For smaller systems, the Saudi Aramco case gives scale: the 1.2×10^3 ton (≈4 MW) tower was ~27% more water‑efficient using TSE, saving 16,501 m^3/yr of makeup (watertechonline.com). Scaling to six similar units would save ~82,505 m^3/yr and even ~82,505 kWh of pumping energy (watertechonline.com), roughly a few thousand USD/yr in water and about $8k/yr in energy for those six units.
Chemical costs often drop when blowdown is reduced. In the softened‑water example, polymeric inhibitor use fell ~60% (www.prochemtech.com). Where reclaimed water replaces potable supply, Bali’s economics show treated effluent can be sold ~0.46 USD/m^3, versus 0.59–1.21 USD for municipal water, implying 20–60% cost reduction for users (mdpi.com).
Capital needs vary. Raising cycles may need little new CAPEX beyond treatment adjustments and controls; installing a 41 gpm softener (~$26k installed) delivered large recurring savings in one case (www.prochemtech.com). Treating 100 gpm of feed water (≈545 m^3/day) for reclaimed sources might cost $100k–$250k in equipment (samcotech.com).
ROI and payback can be rapid. The ProChemTech example had a ~4‑month ROI (www.prochemtech.com). In Bali, selling reclaimed water generated 2–6 billion IDR (≈$0.13–0.40 M) per year (mdpi.com).
Regulatory context matters. U.S. plants face strict effluent limits, and some achieve compliance by reusing once‑through or other streams (power-eng.com). Although Indonesia currently has no specific reuse regulations (proquest.com), planners there have used irrigation‑grade standards (Gov’t Reg. 22/2021) as a surrogate for reuse quality (proquest.com).
What higher‑cycle programs look like
Programs that reliably run at 6–10×C center on feedwater quality and control. Improving feed chemistry — via softening or alternative makeup — can allow higher COCs without fouling, as evidenced by the TSE case above. Many operators also add polishing steps, such as activated carbon, where organics complicate scale/biocide control.
In summary, recent studies and site data indicate that maximizing COC and repurposing alternative waters strongly reduce total water costs and can earn back investment in months to a few years. Source threads include a Saudi Aramco pilot (2020) and peer‑reviewed analyses (J. Envir. Manage. 2024), with detailed citations throughout (sciencedirect.com) (energy.gov) (watertechonline.com) (prochemtech.com) (mdpi.com) (power-eng.com).
