Water Quality: Why it Matters


A system with reducing fluid conductivity will minimize galvanic corrosion, which has taken over the fitting/pipe.

Red flags in water quality shouldn’t be ignored before it leads to system failure

By Bill Hooper

When we have a hydronic system to install and/or put into service, perhaps a question that should have a higher priority on our checklist is to confirm the quality of the fluid that will be used for heat transfer. We are fortunate to live in a country where water quality is generally good, however, over time, fluid quality can break down for a number of reasons.

In an ideal sense, hydronic system fluids (typically water) should contain very little soluble substances (chemical quality), and zero insoluble substances (physical quality). Chemicals that co-exist with the water will certainly be present in both municipal and well water systems—and it can make sense to find out their concentrations. Insoluble substances like oil, grease, particulates from corrosion in the system, or other metal is somewhat manageable—and there are specialized hydronic system components available that can help.

Maintain a healthy system

The truth is that fluid quality—whether plain old H2O or glycol mixtures—is a very important element in the effectiveness and longevity of hydronic systems. We have devices in the boiler room to move the fluid, get the air out of the system, or heat or cool it. All of these are primary considerations… but if the fluid quality is poor, or has become poor, it can affect how well the main system components do their job to bring comfort to the occupied environment.

Since hydronic systems are “closed” and do not introduce freshwater unless there is a leak, it makes it even more important to ensure that the fluid we plan to “re-use” over the life of the system is appropriate in its chemistry, quality, and flow characteristics.

It seems that determining water quality is a back-burner issue, but there are compelling reasons to make it more of a priority…


In smaller systems for residential applications, wet rotor circulators may be the first casualty in poor water quality situations, as these pumps use the system fluid as a lubricant to keep the shaft spinning quietly and efficiently. Hard water, or water with particulates, will not be able to navigate the small spaces between the shaft and rotor without causing some friction and eventual issues that could lead to failure.

In larger or commercial systems, pumps with mechanical seals can be affected. Mechanical seals use a very thin layer of fluid to lubricate between their faces—and since this fluid layer evaporates—remnants of dissolved solids or other issues will come out of the liquid and scratch up seal faces until a failure occurs.

Poor water quality can cause staining on surfaces.

Let’s consider our customers for a moment. Having fluid pumped around a heating system might be a reason for them to choose another type of system for heating/cooling (that doesn’t require fluid). It is a good proactive measure for us, as professionals, to understand how fluid quality affects the system, and the available methods to remedy any issues that arise. Interestingly, an internet search for “water quality in hydronic systems” yields over 1.7 million results, so it will be difficult for the average consumer to gain a good background on this topic and weed through the noise on their own.

Actual quality concerns

Water quality issues can come as small, medium, and large. Small is somewhat benign, and perhaps a cosmetic issue will give us a heads up to potential issues. Medium would be something like degraded heat transfer (inefficient) but still providing heat. Larger issues in water quality can alert us to a problem because a system component has actually stopped working.

It is best to understand the indicators for the small and medium-sized issues in fluid quality before it becomes a system failure—which we all know happens late on a weekend evening on a very cold night!

In some dialogue with one of my colleagues, we had a few interesting observations about water quality problems that can lead up to more significant issues…

  • Particulates or sediment: With metals in the system, there is a chance of corrosion activity precipitating and plugging up screens and filters. Changing the filters and cleaning the screens are easy solutions. The real solution lies in making sure that the water chemistry is optimal to deliver the system performance. In theory, as water delivers its energy and cools, it will tend to want to precipitate certain chemicals in the water/fluid. This can lead to clogs and poor performance.
  • Glycol and glycolic acids: We typically use a mix of water and food-grade glycol to charge or fill a hydronic system. Using the wrong chemical can lead to challenges and an eventual failure. Make sure to use the right chemicals.
  • Iron: With black iron pipes, and other ferrous sources in the water, there is a chance that iron can react with the water/fluid. Removing iron from the water source is critical in maintaining a well operating system.
  • Hardness: Certain chemicals tend to precipitate as they experience temperature and pressure fluctuations. Hardness in the water can precipitate on heat exchangers, and as scale builds up. It takes more energy to heat or cool water—not to mention additional friction losses can affect the design Delta T and reduce comfort levels.

The effect of water hardness on heat transfer efficiency shows up as a scale build-up increasing inside pipes, and the percentage of energy required to heat or cool water increases linearly.

The Water Quality Association and the Battelle Institute have studied this and states that as little as 0.5 mm of hard scale increases fuel costs by 9.4 per cent.

Metal particulates in the system can cause corrosion as seen in this sink.

Generally, a system that has reduced fluid conductivity will minimize galvanic corrosion—and this is the strategy of water treatment for problem systems with this issue.

Total dissolved solids (TDS) and pH

If the water/fluid is high in TDS, then we adjust pH higher to manage corrosion risks. Some of the TDS tend to precipitate and coat surfaces—which fouls the system, screens, and filters. This is especially a concern as temperatures change (lower) on the cool side of the system (return lines).

As water ages, pH tends to change especially as glycol degrades to glycolic acids. Any metal becomes sacrificial and will lead to pinholes, leaks, and failure.

In summary, how we deal with water quality tends to be governed by our specialty. If we are a systems specialist, we tend to care about what affects our components. If we are a boiler specialist, the concern is directed toward heat transfer surfaces. If you are into piping systems, poor water quality can show up in erosion and/or corrosion issue.

We can work to have an overall systems’ view of how fluid quality affects a hydronic system and learn how to effectively deal with the challenges this quality will impose.

Maintaining a good hydronic system fluid quality over time is important, and this is an ongoing maintenance cycle that can provide an opportunity for service work.


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