Poor rinse water quality does not always cause an obvious issue immediately. A can may leave the washer looking acceptable, but dissolved minerals, chemical carryover or fine residues can still affect later stages.

Common rinse-related issues include:

• Water spots after drying
• Staining or surface haze
• Uneven appearance
• Poor coating preparation
• Increased rejects
• Higher customer quality risk
• More frequent troubleshooting

These problems can be frustrating because they may appear downstream from the washer. Production teams may investigate coating, dryer or decoration settings before tracing the issue back to rinse water conductivity.

That is why monitoring matters. Conductivity gives operators a simple, useful signal that rinse water quality is changing before the issue becomes visible at scale.

Reverse osmosis is often central to TSA anodising water treatment because it reduces dissolved salts and minerals from incoming water. This can help produce more consistent water for process make-up and rinsing.

A correctly specified reverse osmosis system may support:

• Low-conductivity process water
• More consistent anodising rinse water
• Reduced mineral carryover
• Better control of final rinse quality
• Lower load on downstream polishing, where used
• More predictable process chemistry

For aerospace applications, the required water quality should be set by the applicable process specification, customer requirement or equipment design. In the Aero Fabrications project, AllWater carried out tap water analysis and RO membrane projections to design an RO plant capable of producing water that met Airbus Spec A standards.

That step matters. RO design should not be based on assumed mains water quality. It should be based on real feedwater analysis, projected performance and the required output quality.

Poor water quality can affect can washer performance in several ways. Some problems appear inside the washer. Others only become visible after drying, decoration or coating.

Common signs include:

• Water spots after drying
• Staining or surface haze
• Inconsistent can brightness
• Blocked or partially restricted nozzles
• Uneven spray coverage
• Scale on heating surfaces or pipework
• Increased chemical consumption
• More frequent manual adjustments
• Higher wastewater load
• Coating or ink adhesion issues
• Increased rejects
• Unplanned cleaning or maintenance stops

These issues often have more than one cause. Dryer performance, washer chemistry, temperature, line speed and maintenance all matter. However, water quality is one of the key variables because it affects every stage of the washer.

A well-designed industrial water treatment system helps control that variable so production teams can focus on the wider process.

Water spots, staining and surface defects

Water spots are often caused by dissolved minerals or contamination left behind when water evaporates. If final rinse water contains too many dissolved solids, those solids can remain on the can surface after drying.

This can lead to visible spots, staining, haze or inconsistent appearance. In a high-speed can manufacturing environment, small defects can become costly very quickly.

The final rinse is especially important because it is often the last water contact before drying and downstream processing. If this rinse is not controlled properly, residues can remain on the surface even when the washer appears to be operating normally.

High-quality rinse water helps reduce this risk. By lowering dissolved solids and controlling conductivity, manufacturers can support a cleaner surface, more consistent drying and fewer visible water-related defects.

Scale, blocked nozzles and uneven spray coverage

Hard water can cause scale inside pipework, spray bars, nozzles, heat exchangers and washer components. As scale builds, it can restrict flow and affect spray pattern consistency.

In a can washer, spray coverage is critical. If nozzles become partially blocked or spray distribution becomes uneven, some cans may not receive enough washing or rinsing contact. This can create inconsistent cleaning, poor residue removal and greater variation between cans.

Scale can also reduce heat transfer, which may affect temperature control and energy efficiency. Over time, this can increase maintenance demands and make the washer harder to keep stable.

A correctly specified water softener can help reduce hardness before it causes scale in the washer or downstream treatment equipment. It may also help protect reverse osmosis membranes, depending on the overall system design.

Suspended solids, aluminium fines and washer contamination

Can washing involves the removal of oils, lubricants, aluminium fines and process residues. If solids are not controlled effectively, they can circulate through the system and increase the load on pumps, tanks, strainers and nozzles.

Suspended solids can also affect rinse quality. Fine particulate contamination may settle in low-flow areas, restrict spray equipment or interfere with downstream treatment stages.

This is where filtration becomes important. Industrial water filters can help remove particulate contamination, protect equipment and support more stable water quality across the washer.

The exact filtration approach depends on the process. A can washer may require pre-filtration, side-stream filtration, cartridge filtration, media filtration or protection upstream of reverse osmosis and deionisation systems.

The aim is not simply to remove visible solids. It is to protect spray performance, reduce avoidable maintenance and maintain consistent process conditions.

Chemical balance and process consistency

Can washer chemistry depends on the correct balance of water quality, chemical concentration, temperature, contact time and flow.

If incoming water quality changes, the chemistry can become harder to manage. High dissolved solids, variable conductivity, excessive hardness, incorrect pH or contamination can all increase chemical demand or reduce consistency.

This can lead to more frequent manual correction, higher chemical consumption and less predictable results. It may also increase the load on wastewater treatment, particularly where oils, surfactants, aluminium or fluoride need to be controlled before discharge.

Good water treatment does not replace process chemistry control. It supports it by providing more consistent make-up and rinse water, so the washer chemistry can perform as intended.

Cooling towers use water to reject heat. As part of that process, some water evaporates. The minerals and dissolved solids in the water do not evaporate with it, so they remain in the circulating water and become more concentrated.

To control that concentration, some water is discharged as blowdown and replaced with fresh make-up water.

If the make-up water has high hardness, alkalinity or dissolved solids, blowdown may need to happen more often to control scale and deposits. This increases water use, discharge volume and chemical demand.

This is where water treatment directly links to WUE. WUE measures the amount of water a data centre uses in relation to IT energy consumption. Lowering avoidable blowdown can help improve water efficiency, provided cooling performance and resilience are protected.

Reverse osmosis can reduce dissolved solids in the make-up water before it enters the cooling tower. This can allow the system to operate at higher cycles of concentration where the chemistry supports it, meaning each litre of water can stay useful for longer before discharge is required.

A useful UK example is NTT’s Hemel Hempstead 3 data centre, reported by Data Center Dynamics. NTT used RO after hard water and high alkalinity caused excess drainage and salt deposition. The system removed more than 95% of dissolved salts and helped reduce WUE from 1.8 l/kWh to 1.2 l/kWh between June 2023 and July 2024.

The lesson is not that every cooling tower needs RO. The lesson is that feedwater chemistry can directly affect blowdown, deposits, chemical use and water efficiency.

Mains water contains dissolved minerals and other naturally occurring constituents. These may include hardness minerals, such as calcium and magnesium, along with sodium, chloride, sulphate, bicarbonate, silica, iron, organic matter and suspended solids.

For general industrial use, this may not always be a problem. For aerospace manufacturing, it can be.

Hardness minerals can form scale on equipment or leave deposits on components. Chlorides and other ions can interfere with sensitive surface processes. Suspended solids can affect rinse quality or block downstream equipment. Variation in incoming water quality can also make process control more difficult.

A process that works reliably using one water supply may become unstable if the water chemistry changes. This is why aerospace manufacturers often need a controlled water treatment system rather than relying on untreated incoming water.

Water quality requirements often become more stringent over time. This may be driven by changes in production processes, tighter product specifications, or updated regulatory standards.

Older systems may no longer be capable of achieving the required purity levels. Even if they continue to operate, they may struggle to maintain consistent results.

This can lead to quality control issues, increased waste, and potential compliance risks.

In these situations, system upgrades or redesigns are often required to introduce additional treatment stages or more advanced technologies.

For high purity applications, advanced demineralisation systems for precise water quality control provide a reliable and efficient solution:

Ensuring water quality aligns with operational requirements is critical for maintaining performance.

One of the most fundamental mistakes in system design is relying on incomplete or outdated water analysis. Water is not a uniform resource. Its composition varies significantly depending on geographic location, supply source, and even seasonal changes.

Designing a system without a detailed and current understanding of water quality introduces risk from the outset. Assumptions about hardness, dissolved solids, or contaminant levels can lead to incorrect system sizing and inappropriate treatment methods.

For example, underestimating hardness levels can result in scaling within boilers or membranes. Failing to identify silica or organic content can lead to fouling that reduces system efficiency and increases maintenance requirements. These issues are often misdiagnosed as operational problems when, in reality, they stem from design decisions made at the beginning.

A comprehensive water analysis should form the foundation of any system design. This includes not only basic parameters such as conductivity and pH but also a deeper understanding of specific contaminants and how they may interact with treatment processes.

Without this level of detail, even the most advanced equipment cannot perform as intended.

Underestimating demand and future capacity requirements

Another common mistake is designing systems based purely on current demand. While this may reduce initial capital expenditure, it often creates limitations as production requirements evolve.

Industrial operations rarely remain static. Increased output, new processes, or changes in product specifications can all place additional demands on water treatment systems. Systems that were not designed with flexibility in mind may struggle to cope with these changes.

In membrane-based processes such as reverse osmosis, exceeding design capacity can lead to reduced recovery rates, increased fouling, and higher energy consumption. Over time, this not only affects performance but also accelerates wear on key components.

Designing for scalability does not necessarily mean oversizing equipment. Instead, it involves selecting systems that can be expanded or adapted as requirements change. This approach ensures that the system remains efficient and reliable over the long term.

Investing in industrial reverse osmosis systems designed for scalable performance allows sites to increase capacity without the need for complete system replacement, reducing long-term costs and disruption.

Electro deionisation is a polishing technology designed to remove residual dissolved ionic species from water following primary treatment. In most cases, this primary treatment is reverse osmosis, which removes the majority of total dissolved solids before the water enters the EDI system.

The purpose of electro deionisation is not bulk salt removal but refinement. It targets low level ionic contaminants that remain after reverse osmosis and reduces them to extremely low concentrations. Under the right conditions, EDI systems can consistently produce water with resistivity values approaching 18.2 MΩ·cm, which is considered ultra-pure water.

An EDI system combines three fundamental elements:

• ion exchange resins that temporarily capture charged ions
• ion selective membranes that allow specific ions to pass while blocking others
• a direct current electrical field that drives ion migration and resin regeneration

These components are arranged within modular EDI stacks that allow water to flow continuously through the system. Because the resins are regenerated electrically rather than chemically, the process does not require periodic shutdowns or chemical dosing cycles.

Ultrafiltration, commonly referred to as UF, is a membrane filtration process used to remove suspended solids, bacteria, viruses, and high molecular weight organic compounds from water.

Ultrafiltration membranes have pore sizes typically ranging from around 0.01 to 0.1 microns. This allows them to retain particles, microorganisms, and colloidal material while allowing dissolved salts and small molecules to pass through.

UF systems operate at relatively low pressure compared to reverse osmosis. Water is pushed across the membrane surface, and clean permeate passes through the membrane pores while contaminants are retained and periodically flushed away.