We use cookies to provide you with a better experience. By continuing to browse the site you are agreeing to our use of cookies in accordance with our Cookie Policy.
The primary concern for poor water quality centers on building occupant health and how to mitigate Legionella and other waterborne pathogens. Yet, plumbing engineers should also maintain good water quality for operational cost savings and improved equipment lifespan.
Poor water quality is commonly caused by minerals, sediments, chemicals and microorganisms, and it can lead to scale formation and corrosion. This reduces the efficiency and mechanical reliability of domestic hot water (DHW) systems and increases the risk of pathogen growth. This can result in higher energy costs, more frequent replacements and increased maintenance and labor expenses.
The financial impact of scale and corrosion can be significant. For instance, thermal efficiency losses in a 100 gallons/minute hot water application can lead to noticeably higher energy costs in a commercial building, potentially amounting to tens of thousands of dollars annually, in some cases. To address this, DHW systems should include adequate anti-scale and corrosion measures coupled with regular monitoring.
Scale reduces DHW system efficiency
One byproduct of poor water quality is scaling. Scale is the accumulation of mineral deposits on surfaces. It can be caused by multiple factors, including scale forming water chemistry, high temperature and pressure changes, which are common in DHW systems. All kinds of scale like calcium carbonate or phosphate can lower DHW systems efficiency. Figure 1 indicates potential DHW system failure points due to scaling.
Scale issues are prominent in many regions throughout the United States because much of the country has hard water. Mineral scale is more likely to form in areas of high heat flux, low flow and high pressure drop. It can occur when there are elevated levels of pH, alkalinity, hardness and phosphate in the water.
Scale is especially prevalent in DHW systems because water heating results in over-saturation of calcium carbonate, which means calcium carbonate is less soluble in hot water. Therefore, as water is heated, calcium carbonate may crystallize and attach to surfaces. Scale is also more likely to form in water that is considered basic, i.e., it has high pH levels.
The ability of the heat exchanger to transfer heat to domestic water is restricted by scale, lowering efficiency. Excessive scale can cause damage to the heat exchanger as well, causing “hot spots” that indicate unequal heat exchange distribution across a metal surface. This equipment can warp, causing failures.
Calcium and magnesium ions must be removed or transformed to address scaling issues in DHW systems caused by hard water. Several proactive methods can be implemented to achieve this goal, including:
• Magnetic and electromagnetic scale reducers. This process transforms the structure of hardness molecules by passing water containing hardness ions through a magnetic field.
• Water softening: This process utilizes ion exchange resin to exchange hardness ions like calcium and magnesium with sodium ion.
• Media-assisted crystallization (MAC). A technology attracting hardness minerals, such as calcium and magnesium, MAC converts those minerals into harmless, crystalized particles that will not stick to pipe and components in water heating systems. Instead, the microscopic crystals break away as they grow, float freely through water and move harmlessly through piping and the water heating system.
A MAC approach is more sustainable than water softeners and additives that use salt and harsh chemicals, produce wastewater or require electricity. The latter options remove important nutrients from hard water and can be more expensive.
Corrosion: A threat to system longevity
While scale compromises system efficiency, corrosion poses an equally significant threat to the longevity of DHW systems. Corrosion occurs when metallic components, such as pipe, tanks and fittings, react chemically with water, oxygen or other substances. Over time, this chemical degradation weakens the system’s structural integrity, leading to leaks, failures and increased maintenance costs.
Two of the primary culprits are the presence of chloride ions and oxidizing chemicals like chlorine or chloramines. Chloride gets into domestic water for different reasons, including but not limited to, the salt used on icy roads and salty water intrusion into underground water resources. Often introduced through the use of chlorine and chloramine, chemical disinfectants get added to water to control microbial growth. Chlorides can lead to significant corrosion issues that can be particularly damaging and difficult to detect.
Chemical disinfectants create a trade-off between pathogen mitigation and protecting system longevity. One alternative is ultraviolet (UV) light disinfection. Unlike chemical methods, UV light is a physical process that inactivates microorganisms without damaging the plumbing system. Moreover, by preventing the formation of biofilms and mitigating microbial risks, UV systems can enhance the reliability and lifespan of DHW systems.
While microbiologically influenced corrosion is also a concern, the role of chlorides and chlorination in corrosion should not be underestimated. Proper material selection, water treatment and alternative disinfection methods like UV light can be essential strategies to mitigate corrosion and ensure the longevity of DHW systems.
Effective measures to maintain water quality
Protecting DHW systems from the adverse effects of poor water quality, such as scale and corrosion, requires a proactive approach. The first step is a comprehensive water analysis.
Regular water analyses help implement and maintain appropriate water treatment practices to ensure system efficiency, reduce maintenance costs, and ensure compliance with health and safety regulations.
Here is a breakdown of the essential metrics to analyze for a comprehensive understanding of water quality on a given premise:
pH: Determines the acidity or alkalinity of the water;
TDS: Measures the total dissolved inorganic material in the water, which impacts the rate of chemical reactions;
Total hardness: Indicates the concentration of calcium and magnesium ions;
Total alkalinity: Represents the buffering capacity of the water, which resists pH changes;
Sulfates and chlorides: Important for assessing corrosion potential;
Free chlorine: Indicates the presence of residual disinfectants;
Total suspended solids: Measures the level of suspended particles.
In situations where microbial contamination is suspected as a contributing factor, testing for microbial contaminants may be a critical next step.
Proactive and reactive water treatment strategies
When evaluating the impact of water quality on systems and materials, a comprehensive analysis of water chemistry, plumbing system materials, and operating conditions is essential. Every site and application presents a unique case requiring careful evaluation.
For example, an application with high chloride levels, low water alkalinity (water chemistry component), the use of 304 stainless steel (material component) and a high-temperature environment (operating parameter component) creates a combination that amplifies corrosion risks. A system-level approach in such cases would recommend reverse osmosis (RO) treatment to reduce chloride levels, along with appropriate post-RO treatment to improve water alkalinity.
While this approach is reactive, proactive strategies can address potential water quality issues before they arise. For instance, a multitreatment system, like the one shown in Figure 2, integrates UV disinfection, sediment filtration and anti-scale technologies (e.g., MAC) to mitigate bacterial risks, solids accumulation and scale formation.
These systems not only offer significant environmental, sustainability and operational savings — avoiding backwashing, salt use and chemical treatments — but also provide proactive plumbing system protection, enhanced water heating efficiency and reduced maintenance costs.
Taking a broader view of water quality in DHW systems — beyond pathogen mitigation — can yield short- and long-term benefits. Often seen as an added expense, investing in water quality measures can, in fact, result in significant savings.
Plumbing engineers who adopt treatment and conditioning measures tailored to specific site conditions can help building owners and facility managers save on annual operating costs, reduce maintenance and replacement needs and improve equipment lifespan.
Armin Madani, a civil and environmental engineer, is a Certified Water Treatment Designer (Water Quality Association) and certified by the American Society of Sanitary Engineering in Legionella safety. He has managed a portfolio of commercial water quality systems at Lync by Watts for the past four years.