Cooling Tower Maintenance Checklist for Building Owners

It is the first hot week of May, and the chiller trips on high head pressure twice before lunch. On the roof, the technician finds sludge in the cooling tower basin, a float valve stuck open and spilling into the overflow, and a chemical feed pump that lost its prime weeks ago. Every contract was in place. Nobody owned the tower as one system.

A complete cooling tower maintenance checklist fixes that. This guide covers components and failure modes, tasks from daily to annual, seasonal start-up and shutdown, water treatment and the questions to ask your vendor, Legionella control, safety, records, efficiency and DMV rules. It applies to open towers and closed-circuit fluid coolers.

Specialist work stays with specialists. A water treatment company runs the chemistry, and qualified HVAC technicians service the mechanical side. Within our HVAC maintenance service, Levaru schedules that work, supervises it and documents it. This guide is general information, not legal or engineering advice.

How does a cooling tower work?

A cooling tower rejects building heat by evaporating a small part of the water that passes through it. Warm condenser water is sprayed over fill, a fan pulls air through, and the cooled water collects in the basin and returns to the chiller.

Water leaves in four ways: evaporation, drift (droplets carried out with the air), blowdown (water drained on purpose to remove dissolved solids) and leaks or overflow. The DOE’s Federal Energy Management Program cooling tower guidance states the balance: make-up equals evaporation plus blowdown plus drift.

A closed-circuit tower runs the building loop through a coil, but spray water still evaporates over that coil. CDC notes that open and closed-circuit towers both release aerosol, need the same basic operation and maintenance, and can both grow Legionella.

Range is the temperature drop across the tower. Approach is how close the cold water gets to the outdoor wet-bulb temperature. A worsening approach at similar load points to scaled fill, clogged nozzles or weak airflow, and the chiller pays: the FEMP O&M Best Practices Guide estimates 2.5% to 3.5% more chiller energy for each degree Fahrenheit of condenser temperature rise.

Which cooling tower components fail, and how?

Each part fails in a predictable way. The table lists the usual failure and what to check.

Component	Typical failure	Check for
Fill	Scale, biofilm, sagging	Fouling, sag, dry spots
Drift eliminators	Gaps, displaced or scaled sections	Seating, damage
Nozzles, distribution basin	Clogged or missing nozzles	Even spray, debris
Cold-water basin, sump, strainer	Sediment, leaks, corrosion	Sludge, strainer, coating
Fan	Blade damage, imbalance, wrong pitch	Vibration, pitch, tip clearance
Motor	Bearing wear, moisture, insulation breakdown	Amps, heat, vibration
Gearbox or belt drive	Oil leaks or contamination; belt wear	Oil condition; belt tension
Fan shaft bearings	Dry or washed-out grease	Lubrication, noise
Make-up valve and float	Stuck open or stuck shut	Manual operation, water level
Blowdown valve, conductivity controller	Fouled probe, stuck valve	Calibration, cycles
Variable frequency drive (VFD)	Faults, heat, moisture	Fault log, enclosure
Basin heater	Failed element, bypassed level control	Test before first freeze
Vibration cutout switch	Disabled, or failed from moisture	Function test

Two failures do outsized damage. A stuck-open make-up valve sends treated water to the overflow unnoticed. A failed blowdown control lets dissolved solids climb until scale forms.

What belongs on a cooling tower maintenance checklist?

Frequencies come from the FEMP O&M guide’s cooling tower checklist, CDC’s cooling tower module, OSHA’s Legionella control guidance and one major manufacturer’s 2026 user manual. “Typical” rows are common practice, not a published rule. Your manual and treatment program override this table.

When	Task	Basis
Daily	Walk the tower: normal sound, no leaks, water flowing, guards in place	FEMP
Daily	Stage cells to load; rotate idle cells	FEMP, CDC
Daily	Read the controller: conductivity, feed pumps, alarms	Typical
Weekly	Test water; adjust blowdown and chemical feed	FEMP
Weekly	Clean the suction screen or strainer	FEMP
Weekly	Operate the make-up float by hand	FEMP
Weekly	Check motor, fan and pump vibration against baseline	FEMP
Weekly	Check for loose fill, leaks, belt and pulley wear	FEMP
Weekly	Flush low-flow pipe runs and dead legs	CDC
Monthly	Confirm bearings are lubricated per the manufacturer	FEMP
Monthly	Check motor supports, blade fasteners, coupling alignment	FEMP
Monthly	Inspect drift eliminators, louvers and fill	FEMP
Monthly	Read make-up and blowdown meters; compare cycles	FEMP; interval typical
Monthly	Review the treatment report against control limits	Typical
Quarterly	Grease fan shaft bearings (or every 2,000 run hours, if sooner)	Manufacturer
Quarterly	Re-tension belts; check fan pitch and motor amps	Manufacturer
Quarterly	Inspect basins and nozzles; drain and flush basins	Manufacturer
Quarterly	Check gearbox oil level and condition	Typical
Semiannual	Clean and disinfect at spring start-up and fall shutdown	OSHA
Annual	Take offline, clean and disinfect (the minimum)	CDC
Annual	Remove scale, dirt and algae from basin, fill and nozzles	FEMP
Annual	Inspect bearings and belts; analyze motor condition	FEMP
Annual	Test the vibration cutout switch; inspect the tower finish	Manufacturer
Annual	Inspect the lockout procedure; review the water management program	OSHA; typical

Seasonal tasks:

Season	Task	Basis
Spring start-up	Clean and disinfect before the tower runs	CDC, OSHA
Spring start-up	Remove debris; inspect basin, fill, nozzles, eliminators	FEMP
Spring start-up	Check belts, alignment, bolts, gearbox oil; turn the fan by hand	FEMP
Spring start-up	Insulation-test motors after a long shutdown	Manufacturer
Spring start-up	Fill, set the float, confirm the make-up valve moves freely	Manufacturer
Spring start-up	Run pumps only and establish biocide residual before fans start	Manufacturer
Spring start-up	Balance flow across the fill and cells; test the vibration switch	FEMP, manufacturer
Spring start-up	Calibrate the conductivity probe; prime feed pumps	Typical
Fall shutdown	Clean and disinfect; lock out fans and pumps	OSHA, CDC, manufacturer
Fall shutdown	Close make-up; drain basin and exposed piping to an approved discharge	Manufacturer; local rules
Fall shutdown	Heat-trace and insulate piping that stays wet	Manufacturer
Fall shutdown	Leave the basin drain open; clean the strainer; cover the fan intake	Manufacturer
Fall shutdown	Lubricate bearings; protect shafts	Manufacturer
Fall shutdown	Test basin heaters and heat trace before the first freeze	Typical

One start-up rule matters most: treat the water before fans run, because fans carry drift out. The wider HVAC calendar is in our HVAC preventive maintenance checklist.

How does cooling tower water treatment work?

A treatment program prevents scale, prevents corrosion and controls biological growth. The three interact: OSHA notes that organic matter and high dissolved solids reduce biocide effectiveness.

Cycles of concentration. Evaporation leaves minerals behind. Cycles compare dissolved solids in tower water with those in make-up water, and FEMP notes the figure roughly equals make-up volume divided by blowdown volume. Higher cycles save water but raise scale and corrosion risk. FEMP says many systems run at two to four cycles, and six or more may be possible.

Conductivity-controlled blowdown. A conductivity controller opens the blowdown valve only above a set point chosen with your treatment specialist. CDC recommends automating blowdown and the feed of anti-scale, anti-corrosion and disinfectant chemicals.

Biocides. Common choices are oxidizers such as chlorine and bromine, plus non-oxidizing products. CDC asks for measurable oxidizer residual throughout each day, and non-oxidizers dosed to label concentration and contact time. OSHA warns that quaternary ammonium compounds may not fully control Legionella and are respiratory sensitizers.

Monitoring. Dip slides and plate counts measure total aerobic bacteria; the Cooling Technology Institute’s Legionella guideline points out they do not detect Legionella. ATP meters give a faster read on microbial activity. Legionella tests are separate: CDC suggests an accredited laboratory and notes culture results typically take 7 to 14 days.

Control limits. pH, conductivity set point, inhibitor levels, biocide residual and microbiological action levels depend on your water, tower materials and chemistry. The vendor proposes them, your water management program adopts them, and every report shows readings against them.

What should you ask your water treatment vendor?

Many published checklists stop at “test the water.” Owners need proof the program works. Ask at award and at each review:

1. What are our control limits, and where are they written?
2. What cycles are we running, and what limits them?
3. Do the meter ratio and the conductivity ratio agree? FEMP says a mismatch means checking for leaks or unauthorized draw-off.
4. What is your cost to treat 1,000 gallons of make-up, and your highest recommended cycles? FEMP suggests choosing vendors on those two measures.
5. Who calibrates the conductivity probe, and where is it logged?
6. When a reading is out of range, who is told, and what is the corrective action?
7. Which biocides do you use, and are we relying on a quaternary ammonium product alone?
8. What microbiological monitoring do you do, and which lab runs Legionella tests?
9. Who cleans and disinfects the tower, to what written procedure, with what PPE?

FEMP adds a candid warning: some vendors may be reluctant to improve water efficiency because the facility would buy fewer chemicals. Make water efficiency an explicit priority.

How do cooling towers relate to Legionella and a water management program?

A cooling tower should have a Legionella water management program even if the rest of the building does not. CDC’s water management program toolkit says devices that spread water droplets should have one, and its first device question is whether the building has a cooling tower.

The program is a written plan, not a chemical contract: hazardous conditions, control limits, monitoring and corrective actions. ASHRAE Standard 188 and Guideline 12 are the framework. Standard 188 sets minimum requirements for legionellosis risk management, and Guideline 12 gives practical guidance, including for cooling towers. Our guide to Legionella water management plans walks through building one.

CDC names four growth factors: sediment and biofilm, temperature, water age and disinfectant residual. Its controls follow:

• Run tower water as cool as practical, below the 77–113°F range most favorable to growth where possible.
• Flush low-flow runs and dead legs at least weekly.
• Automate blowdown and chemical feed.
• Use high-efficiency drift eliminators.
• Locate towers at least 25 feet from building air intakes.

Routine Legionella testing is a program decision. CDC treats cooling tower results below 10 CFU/mL as a sign that growth appears well controlled, while stressing that results do not measure health risk and no level is known to be safe.

For hospitals, critical access hospitals and long-term care facilities, CMS memo QSO-17-30 expects water management plans that consider the ASHRAE standard and CDC toolkit; it does not require water cultures. If you run medical buildings, keep the plan ready for surveyors, and put its reviews on your building compliance calendar.

How often should a cooling tower be cleaned and disinfected?

At least once a year, and plan on twice. CDC calls for offline cleaning and disinfection at least annually. OSHA recommends at least twice a year, normally before start-up and after fall shutdown, and more for heavy biofouling or high Legionella results.

CDC lists four response levels, from online remedial treatment up to offline emergency cleaning and disinfection. ASHRAE Guideline 12 holds the procedures.

The emergency procedure applies when public health officials suspect a link to illness. In outline: stop the heat load and fans, close nearby air intakes, hold a free oxidant residual of 10 ppm for at least 24 hours, drain to the sanitary sewer, physically clean all accessible equipment, then disinfect again, drain and refill. Test before and after, with public health.

This is work for a water treatment professional and a qualified mechanical contractor. For tower cleaning, OSHA calls for the PPE the chemicals require plus, at minimum, a half-face air-purifying respirator with an N-100 cartridge, under a respiratory protection program with medical clearance and fit testing. Ask for a record every time: date, chemical, residual, contact time, components cleaned, who, and photos.

How do you winterize a cooling tower and restart it in spring?

First decide whether the tower runs in winter. A tower serving only comfort cooling can often shut down for the season. One serving a data room, process load or water-side economizer may need to run through DMV winters with freeze protection.

Drained shutdown. Follow the fall rows above. Drain only to an approved discharge; Fairfax County’s fact sheet says winterization and maintenance releases need approval, whether to sewer or storm drain.

Winter operation. A basin heater protects an idle basin; one manufacturer’s manual states that it is not designed to prevent icing while the unit operates. Exposed make-up lines and risers need heat trace and insulation, or draining. A closed-circuit coil needs its own protection: an inhibited glycol solution, or a maintained minimum flow and heat load. One manufacturer warns against routine coil draining because it promotes internal corrosion.

Short wet standby. For shutdowns under 5 days with water left in the system, CDC says to keep the treatment program running and circulate water three times a week.

Spring start-up. Work the start-up rows in order, cleaning and disinfection first, before the first hot week. The building-wide list is in our winter building preparation checklist.

What safety rules apply to cooling tower work?

Tower work combines rotating equipment, height, chemicals and biological exposure. Several OSHA standards usually apply:

• Lockout/tagout. Under 29 CFR 1910.147, servicing requires energy control so fans and pumps cannot start unexpectedly, and employers inspect each energy control procedure at least annually and certify it.
• Fall protection. Under 29 CFR 1910.28, an unprotected side or edge 4 feet or more above a lower level needs guardrails, a safety net or personal fall protection. That often applies on fan decks and tower tops.
• Confined spaces. Under 29 CFR 1910.146, an enterable basin, sump or plenum with limited entry and exit, not designed for continuous occupancy, is a confined space. A hazardous atmosphere during chemical cleaning can make it permit-required.
• PPE and respirators. OSHA’s PPE standards, including 1910.134 for respirators, apply.
• Fire. NFPA 214 covers towers of combustible construction or with combustible fill. A drained tower with plastic fill can burn, so control welding and cutting under a hot-work permit.

These are contractor duties; ask for each program before work starts.

What records should you keep?

Keep enough to prove the program ran. OSHA lists system descriptions, chemical procedures, cleaning and disinfection dates, test results and maintenance work, and CDC asks for logs and service reports on site.

Record	Produced by	When
Water management program and corrective actions	Program team	Current; log revisions
Treatment service reports	Vendor	Every visit
Operator log and meter reads	Building engineer	Weekly to monthly
Microbiological results and lab name	Vendor or lab	Every test
Cleaning and disinfection records	Contractor	Every event
Mechanical work orders, readings, photos	HVAC contractor	Every visit
Lockout inspection certification	Employer	At least annually
Confined-space entry permits	Employer	Keep canceled ones at least 1 year
Equipment data and manuals	Owner	Life of the tower
Submeter and discharge approvals	Owner	Ongoing

Levaru keeps these records in the CMMS included with our management. Each tower gets a QR asset tag, and its preventive-maintenance schedule and photo-documented work orders sit against that asset, visible in the client portal. Owners can export the asset register and work-order history themselves.

How can you cut cooling tower water and energy costs?

Water. FEMP’s example: raising cycles from three to six cuts make-up water by 20% and blowdown by 50%. Meter make-up and blowdown to verify cycles and support sewer credits, and fix leaking floats and overflows. FEMP also lists side-stream filtration for dusty sites, softening where hardness limits cycles, covers on open distribution decks to cut algae, and automated chemical feed on systems over 100 tons.

Energy. Clean heat-transfer surfaces keep condenser water cool. Fans and pumps follow the affinity laws, under which power varies with roughly the cube of speed, so modest fan speed reductions save a lot. A VFD also avoids hard cycling; the FEMP guide says fan motors should start no more than four to five times per hour. Colder water helps the chiller but costs fan energy, so tune the set point as a system.

Our energy management ROI guide shows how to size those savings.

What is different in DC, Northern Virginia and Maryland?

Rules differ by provider; most reward a metered tower.

• District of Columbia. DC Water credits sewer charges for tower water only when DC Water meters are installed: at least a make-up (sewer subtractive) meter and a blowdown (sewer additive) meter, with actual reads on the main meter and submeters. DC Water installs the submeters, and the service must be meter-ready.
• Fairfax County. The county cooling tower fact sheet says a blowdown meter is required for sewer billing under County Code Chapter 67.1, with meters from Fairfax Water. Storm drain discharge needs a state VPDES general permit for non-contact cooling water, and the county notes potable water’s copper and zinc generally exceed what that permit allows, so the water needs treatment first. An unapproved storm drain discharge is an illicit discharge; the county’s stormwater ordinance allows civil penalties up to $32,500 per violation, each day a separate offense.
• Maryland (WSSC Water). WSSC defines a submeter as a meter that measures water not returned to its sewer. Ask WSSC how that applies to tower make-up and blowdown.
• Elsewhere in Northern Virginia. Ask your provider whether it offers a submeter or evaporation credit.

The make-up line also needs the backflow protection your water authority requires; see our backflow testing guide. OSHA notes some states mandate cooling tower inspection, testing, cleaning and disinfection, and flags registration rules in New York State and New York City. Confirm current local rules with DC Health, the Maryland Department of Health or the Virginia Department of Health. Chiller plant efficiency also affects results under building energy performance standards in DC and Maryland.

When should you repair or replace cooling tower components?

Most towers need parts long before replacement, so decide part by part.

• Nozzles. Replace cracked or missing ones at the next service.
• Drift eliminators. Replace damaged sections. OSHA notes older towers can be retrofitted with high-efficiency eliminators.
• Fill. Clean light fouling. Replace fill when scale or biofilm will not come out, or when packs sag or collapse.
• Fan, gearbox and motor. Decide on condition, vibration trends and failure history.
• Basin and casing. Local corrosion and leaks can often be repaired or lined. Widespread structural deterioration is a replacement signal.

For the whole tower, FEMP advises comparing every retrofit and operating option with the cost and benefit of a new tower. The logic in our commercial HVAC repair-or-replace guide applies, and the result belongs in your capital plan.

Frequently asked questions

How often should a cooling tower be cleaned and disinfected?

CDC calls for offline cleaning and disinfection at least once a year. OSHA recommends at least twice a year, normally before spring start-up and after fall shutdown. Heavy biofouling or high Legionella results call for more, and new or long-idle towers should be cleaned and disinfected before they run. Your water management program should state the interval and procedure.

Who is responsible for cooling tower water treatment?

Treat it as the owner’s responsibility, even when contractors do the work; CDC writes its water management toolkit for building owners and managers. A water treatment vendor typically designs the chemistry and reports readings. An HVAC contractor services fans, drives and the basin. The program team sets limits and corrective actions, and a facility manager should read both reports together.

Does every cooling tower need a Legionella water management program?

CDC’s toolkit says devices that can spread water droplets, including cooling towers, should have a water management program even when the building itself does not need one. ASHRAE Standard 188 and Guideline 12 provide the framework. CMS expects documented plans from hospitals, critical access hospitals and long-term care facilities, and some states and cities add their own rules.

How do you winterize a cooling tower?

For a seasonal shutdown, clean and disinfect, lock out fans and pumps, close the make-up valve, drain the basin and exposed piping to an approved discharge, leave the drain open, and heat-trace any piping that stays wet. For winter operation, remember basin heaters protect only an idle basin, protect exposed lines, and follow the manufacturer’s cold-weather instructions.

Does a closed-circuit cooling tower need the same maintenance?

Yes, on the spray side. CDC states that open and closed-circuit towers need the same basic operation and maintenance, both release aerosol, and Legionella can grow in both. The coil keeps the building fluid away from the air, but the spray water over it still evaporates and needs treatment and cleaning. The coil also needs freeze protection.

Can you get a sewer credit for cooling tower evaporation in the DMV?

Often, if the tower is metered correctly. DC Water credits sewer charges only with DC Water make-up and blowdown meters on the tower. Fairfax County bills commercial sewer on actual water use, and some customers separately meter cooling water. WSSC Water uses submeters for water not returned to its sewer. Confirm current requirements before you plumb meters.