Water pipe corrosion is the deterioration of piping materials due to chemical reactions with water and the surrounding environment. This degradation compromises the structural integrity of the plumbing system. The chemical breakdown releases metal particles into the water supply and can lead to costly property damage over time. Understanding the causes and consequences of this issue is the first step toward maintaining a safe and reliable home water system.
Chemical and Environmental Causes
The primary drivers of internal pipe corrosion are factors related to water chemistry, which makes the water aggressive toward metal surfaces. Water acidity, measured by its pH level, is a major contributing factor. Water with a pH below 7 is considered acidic and actively dissolves metal pipes. This acidic condition accelerates the deterioration of materials like copper and galvanized steel, often leading to deep pitting and leaks.
Another element is the presence of dissolved gases, particularly oxygen and carbon dioxide. Dissolved oxygen is highly corrosive and speeds up the oxidation process, resulting in the formation of rust and localized pitting on the interior pipe walls. Carbon dioxide dissolves in water to form weak carbonic acid, which further lowers the pH and enhances the water’s corrosive nature.
The mineral content of water also plays a role in determining its corrosive potential. Water with low mineral content, often referred to as soft water, is more aggressive because it lacks the protective mineral scale that naturally forms on pipe interiors. Also, when two different metals, such as copper and galvanized steel, are connected, galvanic corrosion occurs. The water acts as an electrolyte, causing the more chemically active metal to corrode at an accelerated rate to protect the less active one.
Identifying Signs of Corroded Pipes
The first noticeable sign of internal pipe corrosion is often a change in the water’s appearance or taste. Discolored water is a clear indicator of metal leaching. Brown, orange, or rusty red hues point toward the corrosion of iron or galvanized steel pipes. Water that appears blue or green signals the dissolution of copper from the interior plumbing lines.
A metallic taste or odor in tap water is another common symptom, caused by elevated levels of iron or copper particles released from the deteriorating pipes. A bitter taste is characteristic of copper contamination, while a sweet taste can indicate the presence of lead. These symptoms are usually more pronounced after the water has been sitting unused in the pipes for several hours, such as in the morning.
Corrosion and mineral buildup inside the pipes also physically restricts the flow of water, leading to a loss of water pressure, especially when multiple fixtures are used simultaneously. On exposed plumbing, visible corrosion appears as a reddish-brown scale on iron pipes or a bluish-green powdery substance on copper pipes, often near fittings or joints. Unexplained damp spots or pinhole leaks on walls and ceilings may signal that corrosion has breached the pipe wall.
Consequences for Health and Property
The most serious consequence of water pipe corrosion is the leaching of heavy metals into the drinking supply, creating health hazards. Lead, which may be present in older pipes, solder, or brass fixtures, is a neurotoxin with no safe level of exposure. In children, lead exposure is linked to central nervous system damage, lowered intelligence quotient (IQ), and behavioral and learning difficulties.
While copper is a trace element, its concentration in drinking water can become harmful when pipes corrode excessively. Acute exposure to high levels of copper can trigger gastrointestinal distress, causing nausea, vomiting, and abdominal pain. Chronic exposure to elevated copper levels can lead to severe health issues, including liver and kidney damage.
Corrosion also results in damage to the home’s infrastructure, beginning with reduced flow capacity. The buildup of rust or mineral scale, known as tuberculation, narrows the effective diameter of the pipes, restricting water flow and forcing appliances to operate less efficiently. Pinhole leaks, caused by localized pitting corrosion, allow water to seep into the building structure over time. This hidden moisture creates an environment for mold and mildew growth, which can compromise the structural integrity of walls, ceilings, and flooring.
Strategies for Mitigation and Prevention
Municipal water systems often implement corrosion control treatment to reduce the aggressiveness of the water before it reaches individual homes. This involves adjusting the water’s pH level and adding a corrosion inhibitor, such as orthophosphate. The inhibitor reacts with metal ions to form a stable, protective mineral barrier on the pipe interiors. This layer minimizes the leaching of metals like lead and copper into the water supply.
Homeowners can take simple steps to reduce their exposure to leached metals, particularly by flushing stagnant water. Running the cold water tap for a few minutes, or until the water feels noticeably colder, helps flush out water that has been sitting in contact with the pipes. This action should be performed first thing in the morning or anytime the water has not been used for several hours.
For added protection, especially when lead is a concern, installing a point-of-use (POU) filter at the tap is an effective short-term solution. Filters certified under NSF/ANSI Standard 53 are proven to remove both dissolved and particulate lead from drinking water. When pipe replacement is necessary, modern non-metallic materials offer the best long-term prevention against corrosion. Durable plastic options like cross-linked polyethylene (PEX) and polyvinyl chloride (PVC) are preferred because they do not contain metals that react with water.