The condition of a home’s plumbing has a major impact on water quality but is often a bit of a mystery. After all, most of us never see the inside of our pipes! Or even think about them!

The interaction between your pipes and the water flowing through them can be a complex mixture of physical, chemical, and biological processes. We’ll be focusing on two of the major processes that can impact your pipes: corrosion and scaling. What are they? How are they related? And what can you do to prevent expensive failures in your pipes and fixtures? We’ll tease out these subtleties below.

Corrosion is a process that occurs when there is an electrochemical reaction between a metal (in our case, the pipe wall) and water. The result of corrosion is the oxidation of metal on a pipe wall, after which metal is released into the water or reacts with components present in the water, creating a new compound that adheres to the pipe wall.

The best known case of corrosion is the type that releases metals into the water because the metals are often a health concern. Plastic and cement pipes can leach compounds into water and degrade as well, but the following discussion focuses on metal pipes Around two-thirds of municipal water infrastructure is made of legacy materials like iron and steel and, though the use of materials containing lead was banned in public drinking water system in 1986, there remain over 9.7 million lead service lines connecting homes to the municipal drinking water pipes. Household plumbing and fixtures can pose corrosion risks as well, especially in older homes, as they may be made of a variety of metals and/or alloys.

The second type of corrosion does not result in metal release from the pipe wall. Instead, the corroded metal stays on the pipe wall as newly bound up metal and pipe material. This newly bound up metal is a type of scale. Scale is simply the build up of minerals and other compounds on pipe walls. So yes–it is confusing but correct–corrosion can result in scale! Let’s call this ‘oxidation scale’. While corrosion can occur without scale and scale can exist without corrosion, they often occur together and feed into one another. The "Back to scale–what is it, again?" section below will dive deeper into scale.

Corrosion can manifest as a build up of material inside the pipe (oxidation scale), the thinning or rupturing of pipe walls, or both! Oxidation scale typically looks rusty and can be somewhat smooth (like in the lead pipe in Figure 1), or lumpy (like the tuberculation–or formation of lumps of metal–in the iron pipe in Figure 2). ‘Pinhole leaks’, tiny holes in the pipe wall, are another common consequence of corrosion and are known to occur in copper pipes (Figure 3).

(Terese Olson, Researchers estimate amount of lead released from Flint water pipes). Figure 1: Interior of a lead service line from Flint, MI.

(Shutterstock). Figure 2: Tuberculation in a corroded iron pipe.

There are three common types of corrosion: uniform, non-uniform or localized, and galvanic. Uniform corrosion occurs across the entire pipe wall, while non-uniform corrosion occurs in a much more localized fashion due to either impurities in the pipe materials or localized water quality differences (e.g., tuberculation and pinhole leaks). Galvanic corrosion is a bit of a different mechanism–galvanic corrosion can occur in places where dissimilar metals are joined together, such as lead solder joining copper pipes. All three of these types of corrosion can result in the build up of oxidation scale or the release of metals from the pipe wall, depending on pipe materials and water quality conditions.

If pipes are left to corrode for long periods of time, they can eventually clog with oxidation scale and/or be eaten away to the point of rupturing. In addition to having to replace your plumbing, you can imagine the types of problems that could cause in your house!

In addition to damaging your plumbing, corrosion can impact the aesthetics of your water and your health. First, corrosion can cause noticeable changes to the taste and color of your water. For example, a rusting iron pipe may cause your water to take on a brownish color and metallic taste if the rust is sloughed off into the water. Another potential consequence of corrosion is the release of toxic metals, which are usually tasteless, colorless, and odorless in drinking water. Lead doesn’t cause taste, color or odor problems, but can be highly toxic in low concentrations.

Like we mentioned above, scale is the build up of minerals and other compounds on the inside of pipes. This is likely to occur in pipes of any material: metal, plastic, cement, etc. Ideally, there is a moderate amount of scale in pipes to protect them from corrosive conditions that result in metal release, but it becomes problematic when scale gets excessive.

Scale looks differently depending on what process is forming it and what else is in the water. Scale created by or downstream of corrosion often looks rusty (Figure 4), while scale exposed to manganese can look black. On the other hand, scale primarily made up of calcium carbonate (or limescale) has a whitish color (Figure 5).

(Shutterstock). Figure 4: A new pipe joint and a joint after years of use, containing significant amounts of scale.

(Shutterstock). Figure 5: Pipes with excessive limescale build up.

There are two main types of scale that may form in pipes. The first is the one we briefly discussed in the corrosion section, which we’re calling ‘oxidation scale’. Oxidation scale is caused by the direct reaction of the water and the pipe material. When oxidation scale is insoluble and durable, it is protective for pipes and prevents further corrosion; this specific type of oxidation scale is referred to as a passivating film. However, when oxidation scale is highly soluble and friable, it can become problematic. These unstable scales can slough off of the pipe wall, releasing corrosion products into the water; they can also become thick enough to impact the flow of water through pipes. In addition, these scales do not necessarily protect pipes from corrosion and, rather, allow corrosion to continue at the surface of the pipes, thereby continuing to build up.

The second type of scale that can be present in pipes is caused by the deposition of materials from the water onto the pipe walls. Let’s call this ‘deposition scale’. This type of scale can result in what we call excessive scale–which can cause problems for your plumbing and appliances. The most well known cause of excessive scale is calcium carbonate, or limescale.

As we’ve discussed above, a moderate amount of scale can be helpful for your pipes, protecting them from corrosion and other damage to the pipe walls. However, when there’s too much scale in your pipes, it becomes a problem. If scale is allowed to build to excessive amounts, it can eventually clog your pipes and result in costly repairs.
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The conditions that cause scale in your pipes also cause scale to build up on other things, like appliances and fixtures. Over time, this can reduce the service life of your appliances, which can get expensive because it also increases the frequency with which you have to replace them. Scale build-up is most common in appliances that heat water (Figure 6). The white spots you may be familiar with are typically limescale, which becomes less soluble (thus deposits from water onto a surface) as water temperature increases.

(Shutterstock). Figure 6: The heating element of a water heater being replaced after excessive scale buildup rendered it nonfunctional.

In addition to potentially damaging pipes and appliances, excessive scale can also be a nuisance. The water quality conditions that cause limescale, namely high water hardness, can cause issues with skin and hair: dry and brittle hair, dry skin, and even the exacerbation of eczema.

The short answer is that there is no easy way to know for sure whether your pipes are safe from excessive scale or corrosion. However, we’ve identified a variety of indicators that you can test for which can help you get a pretty good idea of what’s going on.
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The first thing we look at when thinking about the conditions of pipes is the water flowing through them. The table below shows five water quality characteristics that SimpleLab identified as the most important and readily measurable indicators of pipe health. Each characteristic has a range of values that we recommend to maintain optimal pipe conditions.

There are many other factors that can shed light on the potential for corrosion and scaling in pipes, including the water’s temperature, disinfectant type, dissolved oxygen, stagnation time and the pipe material and age. These factors are much harder to assess when compared to the five parameters we use as indicators of pipe health.

Now that we’ve reviewed some of the factors that can impact your pipes, let’s discuss strategies we can use to prevent excessive scaling and corrosion.

If you rely on a utility, it is likely that your water already contains a corrosion inhibitor, which creates a passivating film inside pipes that protects them from harmful corrosion (Figure 7). However, there are many different types of corrosion inhibitors and no guarantee that the most appropriate one is being used or has made it all the way to your household plumbing. And, of course, there are many folks who do not use utility water. Therefore, we recommend testing, treating, and monitoring. In addition, you should consult a plumbing professional if you’re experiencing any issues with your plumbing system.

(Rebecca Williams / Michigan Radio: Here's what drinking water pipes look like with and without corrosion control). Figure 7: Drinking water pipes without corrosion inhibitor (far left) and with corrosion inhibitor (three remaining pipes with white coating).

Treatment options are either point of entry (POE) or point of use (POU) systems. For mitigating problems with scaling and corrosion, a POE system is required. A POE system treats water as soon as it enters your house and will thus protect your on-site plumbing and fixtures, whereas a POU system treats the water at the point of use (for example, an under-sink unit or pitcher filter) and will not protect your plumbing system.

The type of treatment you install depends on which of the water quality characteristics need adjusting, as well as any other health or aesthetic concerns you identify through testing.

A few example treatments that address potential corrosion or excessive scaling are shown in the table below.

After you’ve tested and installed treatment, you’ll want to conduct follow-up testing to ensure your treatment is working over time.

Our experts can help you choose the best testing routine and household level treatment technology to suit your needs–so contact us today to get started!