Regional threats to U.S. water infrastructure: How coatings can help

Every year, U.S. municipalities spend thousands (sometimes millions) treating water that never should have entered their systems or repairing structures that fail far earlier than expected. Across the U.S., two different forces quietly degrade municipal water infrastructure every day: corrosion and infiltration. The first, driven largely by hydrogen sulfide–induced acid attack, thrives in warm, wet climates where sewer gases remain more active. The second, infiltration, proves most destructive in areas that have a high-water table and in older systems where aging brick and concrete allow groundwater to enter the system.

Both threats carry steep costs. They weaken structures, shorten service life and increase treatment expenses for utilities already working within tight budgets. Rehabilitation measures that fail to address these factors will not be able to function as long-term fixes. In some instances, product systems cannot withstand the corrosive environment or lack the necessary physical properties to bond to the host structure, thereby resisting hydrostatic pressure in the long term. By understanding how these processes differ by region and asset type, municipalities can better tailor their inspection, maintenance and protective coating strategies so they can act before the damage escalates.

Environmental conditions and asset degradation

Corrosion in warm, humid environments

Sewer systems produce hydrogen sulfide (H₂S) as organic matter breaks down. While the gas itself is corrosive, the real damage occurs when bacteria on the interior surfaces oxidize H₂S into sulfuric acid. Concentrations as low as 1% acid can aggressively attack concrete.

Conditions that accelerate this cycle, including heat, high humidity and stagnant or turbulent flows, remain common in southern states. Warmer ground and air temperatures increase gas production, while both low-flow “stagnant/septic” and high-turbulence segments of a collection system can elevate H₂S levels. In hot climates, even relatively new systems can show measurable deterioration within a few years without protection.

Infiltration in older, cooler systems

Infiltration remains a problem across the U.S., particularly in areas with high water tables or those experiencing elevated rainfall levels. In the Northeast and upper Midwest, cooler temperatures slow gas production, so sulfide-induced corrosion may be less aggressive. Meanwhile, older infrastructure, especially brick manholes and clay pipes, faces a different threat: destabilization from excessive groundwater infiltration.

Although sulfide-induced corrosion is less aggressive in cooler climates, older brick infrastructure faces a related but distinct challenge: infiltration-driven degradation of mortar joints. While the bricks themselves are resistant, groundwater infiltration can introduce acidic conditions that degrade the Portland cement mortar. As the mortar deteriorates, joints open, creating pathways for groundwater to enter.

Each gallon of groundwater that enters a system must be treated as if it were sewage, driving up operating costs. For instance, a single manhole leaking at one gallon per minute can add more than 1,400 gallons per day to treatment volumes, resulting in more than $1,000 in annual costs for just one leaking manhole at typical treatment rates. Scale that across dozens or hundreds of leaking structures, and the cost impact becomes substantial.

In high-water-table cities like Houston, some manholes can leak at 10 gallons per minute or 14,000 gallons a day year-round, costing an estimated $10,000 per manhole annually just for treatment. Infiltration also carries hidden structural costs, washing fine soils into the system, destabilizing bedding, and increasing the risk of sinkholes or pipe misalignment.

Corrosion vs. infiltration: Mechanisms and risks

Sulfide-induced corrosion begins with gas production in sewage, intensifying where flow conditions trap waste or increase turbulence. When H₂S contacts moist surfaces, bacteria convert it into sulfuric acid that dissolves cement paste, exposing and weakening aggregate. Without intervention, structural cross-section loss can occur within a few years.

Infiltration adds to the internal corrosion problem. Instead of just surface material loss from within a structure, external water forces its way through. Infiltration can wash in fine soils, destabilizing bedding material, structural damage and increasing the risk of sinkholes or pipe misalignment. It can also bring in sediment that settles in lines, causing blockages and increasing cleaning costs.

Both mechanisms degrade service reliability, but they demand different inspection priorities. Corrosion requires monitoring for surface pH changes and section loss, while infiltration often reveals itself through flow monitoring, dye testing or visual inspection during wet weather.

Tailored strategies by climate, material, and structure

A single “best” rehabilitation method does not exist. Instead, the most effective strategy considers the structure’s material, its environment and the dominant degradation mechanism.

High corrosion coating strategies

For high-corrosion environments (e.g., warm southern systems, force mains with turbulence, and interceptors with long detention times):

• Specify coatings resistant to low-pH conditions (pH ≤ 1).
• Prioritize fully bonded systems to prevent acid migration behind the coating.
• Consider epoxy-based structural linings where added mechanical strength proves beneficial.

High infiltration coating strategies

For high-infiltration environments (e.g., older brick manholes, and high groundwater areas):

• Stop active leaks before surface preparation using injection grouts or other sealing methods.
• Use fiber-reinforced or polymer-modified repair mortars to rebuild lost sections.
• Apply a high-adhesion protective coating or lining to create a monolithic barrier against corrosion and future leaks.

Composite systems, where a polymeric lining follows a cementitious rebuild, offer the best of both worlds. That approach includes structural restoration and additional reinforcement plus long-term chemical protection. The physical properties of structural epoxy linings used in these systems often exceed three times the compressive and flexural strength of standard construction-grade concrete, adding measurable load-bearing capacity.

The role of chemical-resistant, high-adhesion, structural reinforcing coatings

Advanced protective coatings and linings do far more than resist corrosion. The most effective systems for wastewater environments share these traits:

• High chemical resistance: Ability to withstand continuous exposure to low-pH environments and intermittent chemical spikes. Epoxy formulations remain a mainstay.
• High adhesion: Epoxies are extremely moisture tolerant, which adds to their high bond strength and enables them to resist hydrostatic pressure from external groundwater. Bonded systems resist “blow-off” or bypass pathways that unbonded liners cannot withstand long-term.
• Thickness and structural contribution: At thicknesses of 125 mils and above, with excellent physical strengths and bond characteristics, certain epoxy linings can contribute to the structural integrity of the host asset, resisting both internal and external loads.

Inspection and quality assurance

Regardless of climate or material, coating performance begins with surface preparation. Industry standards from ASTM, ICRI, and AMPP stress that 90% of coating failures stem from poor preparation. A robust quality assurance/quality control (QA/QC) plan should include:

• Leak elimination verification before coating.
• Surface profile measurement (e.g., CSP 3 to 5 for cementitious substrates).
• pH testing to ensure a neutral surface ready for bonding.
• Wet and dry film thickness checks to confirm minimum specified coverage.
• Holiday testing to detect pinholes or discontinuities.
• Pull-off adhesion testing to verify bond strength.

These steps protect the coating investment and any prior rehabilitation work, such as structural patching or infiltration sealing.

Cost implications and lifecycle perspective

The financial case for proactive corrosion and infiltration control remains compelling. For infiltration, each untreated leak compounds operating costs year after year. For corrosion, unprotected deterioration can necessitate complete structural replacement far earlier than planned.

By combining preventive coatings with sound rehabilitation, municipalities can double the service life of assets, reduce emergency repairs, and free up budget for planned improvements. Skipping corrosion protection after rehabilitation is like rebuilding a classic car and refusing to paint it. The work will not last.

Act now: A regional, asset-specific approach

Different mechanisms may drive corrosion and infiltration, but both threaten the long-term performance and financial stability of wastewater infrastructure. Address them through a regional, asset-specific approach:

• In the South and other warm, humid regions, focus on acid-resistant, fully bonded systems to counter sulfide-induced corrosion.
• In older northern systems, prioritize infiltration control and monolithic sealing or a single, seamless coating layer to protect against groundwater entry.

With inspection, proper repair materials and a high-performance protective coating system, utilities can extend asset life, reduce long-term costs and protect the communities they serve. Make these changes before the next budget year and not after the next failure.