What Are the Types of Commercial Water Treatment?
Commercial water treatment falls into three main categories: physical treatment (filtration, softening, reverse osmosis), chemical treatment (scale inhibitors, corrosion inhibitors, biocides, pH control), and biological control (managing Legionella, biofilm, and microbiological contamination). In practice, most commercial building water systems require a combination of all three.
The Three Categories of Commercial Water Treatment
1. Physical Treatment
Physical treatment processes remove or modify constituents in the water by physical means - without adding chemicals. The principal physical treatment methods used in commercial and industrial buildings in Ireland are:
| Method | What It Does | Commercial Application |
|---|---|---|
| Ion exchange softening | Removes calcium and magnesium ions (hardness) by exchanging them for sodium ions on a resin bed | Boiler feedwater; catering equipment; laundries; process water pre-treatment |
| Reverse osmosis (RO) | Forces water under pressure through a semi-permeable membrane that removes dissolved solids, salts, and most contaminants | Pharmaceutical purified water; food and beverage process water; electronics manufacturing |
| Filtration (multimedia, sand, activated carbon) | Removes suspended solids, turbidity, chlorine, and organic matter | Pre-treatment ahead of softener or RO; process water quality improvement |
| Ultraviolet (UV) disinfection | Inactivates bacteria and viruses by exposing water to UV light at 254nm wavelength without chemical addition | Food and beverage process water; pharmaceutical water loops; drinking water polishing |
| Deaeration | Removes dissolved oxygen from boiler feedwater by vacuum or thermal means | Steam boilers and high-temperature hot water systems; prevents oxygen pitting |
2. Chemical Treatment
Chemical treatment is the addition of specific reagents to the water to alter its chemistry and prevent scale, corrosion, or biological growth. It is the most common form of ongoing water treatment in commercial building services systems because it can be applied continuously through automatic dosing equipment, is adjustable in response to changing water conditions, and can be formulated for the specific metallurgy and operating conditions of each system.
| Chemical Type | Function | Typical Systems |
|---|---|---|
| Scale inhibitors (phosphonates, polyacrylates) | Prevent calcium carbonate and other mineral scales from forming on heat transfer surfaces | Boilers, cooling towers, heat exchangers, closed loops |
| Corrosion inhibitors (molybdate, nitrite, azoles, phosphates) | Form a protective film on metal surfaces that retards electrochemical corrosion | Closed loop heating and chilled water; cooling towers (copper/steel systems) |
| Oxidising biocides (chlorine, bromine, chlorine dioxide) | Kill bacteria including Legionella by oxidising cellular components; rapid action, limited residual | Cooling towers and evaporative condensers (primary Legionella biocide); cold water systems (shock treatment) |
| Non-oxidising biocides (isothiazolinone, glutaraldehyde, DBNPA) | Kill bacteria by different mechanisms to oxidising biocides; better biofilm penetration; used in rotation to prevent resistance | Cooling towers (alternated with oxidising biocide); closed loops with biofilm risk |
| Oxygen scavengers (sodium sulphite, DEHA, hydrazine alternatives) | Remove dissolved oxygen from boiler feedwater to prevent pitting corrosion | Steam boilers; LTHW/MTHW/HTHW systems; closed systems without deaeration |
| pH adjusters (caustic soda, acid, alkalis) | Maintain water pH within the target range for the system type | All system types; critical for corrosion control (most metals corrode fastest at pH extremes) |
| Dispersants and anti-foulants | Prevent suspended particles, corrosion products, and biofilm from adhering to surfaces; keep systems clean | Cooling towers; boilers; closed loops with high iron or suspended solids |
3. Biological Control
Biological control addresses the risk posed by bacteria, algae, fungi, and other microorganisms in commercial water systems. The most significant biological risk in Irish commercial buildings is Legionella pneumophila - the causative agent of Legionnaires disease - which colonises water systems at temperatures between 20°C and 45°C and is dispersed through aerosols created by cooling towers, showers, taps, and any system that creates fine water droplets.
Biological control is not simply biocide dosing. A complete biological control programme includes:
- 1 Temperature managementMaintaining hot water at storage temperature of 60°C and distribution above 50°C; maintaining cold water below 20°C.
- 2 Physical cleaningRemoving sediment, scale, and biofilm from tanks, cooling tower fill, and water system surfaces that provide habitat for Legionella.
- 3 Chemical disinfectionBiocide dosing programmes appropriate to the system type; shock disinfection where required.
- 4 Microbiological monitoringWater sampling from designated points at appropriate frequency, analysed by INAB-accredited laboratory.
- 5 Risk assessment and written schemeThe regulatory framework that governs how all biological control measures are documented, reviewed, Legionella risk assessment, and implemented.
Which Treatment Types Apply to Each Commercial Water System?
| System Type | Physical Treatment | Chemical Treatment | Biological Control |
|---|---|---|---|
| Steam boiler | Softening (feedwater); filtration; deaeration | Scale inhibitor, corrosion inhibitor, oxygen scavenger, pH control, anti-foam | Generally low biological risk (high temperature); monitored by feedwater microbiological testing |
| Low/medium/high temperature hot water (LTHW/MTHW/HTHW) | Filtration; softening of make-up water | Corrosion inhibitor, scale inhibitor, pH control, oxygen scavenger (closed) | LTHW systems below 50°C are a Legionella risk zone - temperature management and sampling required |
| Closed chilled water / fan coil | Filtration of make-up water | Corrosion inhibitor, pH control, biocide (low dose for closed system) | Periodic microbiological sampling; biofilm management where temperatures favour growth |
| Cooling tower / evaporative condenser | Side-stream filtration; make-up water softening | Oxidising biocide, non-oxidising biocide (rotation), scale inhibitor, corrosion inhibitor, dispersant | Primary Legionella risk system; continuous dosing; monthly sampling; HPSC registration; risk assessment |
| Cold water storage and distribution | Filtration; softening (where water hardness is very high) | Shock chlorination or chlorine dioxide (disinfection events) | Annual tank clean; temperature monitoring; Legionella sampling; risk assessment |
| Process water (food/pharma/manufacturing) | RO, deionisation, filtration, UV (as required by specification) | Sanitisation chemicals appropriate to product specification; CIP chemicals | Microbiological testing against product/process specification; validated cleaning procedures |
Frequently Asked Questions
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What is the most common form of water treatment in commercial buildings in Ireland?
Chemical treatment - specifically the ongoing dosing of corrosion inhibitors, scale inhibitors, and biocides into closed loop heating systems, cooling towers, and boiler systems - is the most widely used form of water treatment in Irish commercial buildings. It is continuous, adjustable, and can be managed by automatic dosing equipment on a regular service schedule. Physical treatment (water softening) is the second most common, particularly in Dublin and Leinster where mains water is very hard. -
Does a commercial cooling tower in Ireland need more than one type of biocide?
Yes. Current best practice under HSG274 Part 1 and the HPSC guidance on Legionella control in cooling towers requires the use of both oxidising and non-oxidising biocides in a rotating programme. Using a single biocide type continuously creates a risk of resistance development and does not address all components of the microbiological risk. Halpin & Hayward designs biocide rotation programmes appropriate to the specific system and risk profile of each cooling tower installation. -
Can we treat the Legionella risk in a cooling tower with chemistry alone, without cleaning?
No. Chemical treatment manages the ongoing Legionella risk in a well-maintained cooling tower, but it cannot substitute for physical cleaning. Scale, biofilm, and fouling material on fill pack and basin surfaces harbour bacteria in a protected environment that biocides have limited ability to penetrate. Quarterly cleaning of the tower basin and annual cleaning of fill pack (or more frequently in high-fouling environments) is required alongside the chemical programme. HSG274 Part 1 is explicit on this point.
Discuss Commercial Water Treatment Requirements
Halpin & Hayward provides commercial and industrial water treatment for boilers, cooling towers, closed loop systems, process water and commercial water softening across Ireland.