&EPA

United States
Environmental Protection
Agency

Distribution System Water Quality

Impact of Corrosion Control on Disinfectant Residual



Corroding metals and associated corrosion products in finished water can react with disinfectants, causing areas of low
disinfectant residual in the distribution system. Low disinfectant residual can increase the potential for microbial growth including
the growth of opportunistic pathogens. Effective corrosion control treatment and distribution system maintenance can reduce
corrosion products on the metal surfaces and in the bulk water and sediment, and lower disinfectant demand, allowing for better
control of microbial growth and other benefits. This fact sheet is part of EPA's Distribution System Toolbox developed to
summarize best management practices that PWSs, particularly small systems, can use to maintain distribution system water
quality and protect public health. For information about corrosion control to reduce lead concentrations, please see:
https://www.epa.gOv/dwreginfo/lead-and-copper-rule-implementation-tools#CCT.

How Pipe Corrosion Affects Disinfectant Residual

•	Exposure of metal pipes to drinking water may cause corrosion and metal release
into the water if pipes are not protected. Effective corrosion control can reduce
the degree of corrosion and by-product build-up by decreasing disinfectant
demand, thereby increasing disinfectant residual.

•	Poor corrosion control can result in areas of the distribution system with low
disinfectant residuals; thick corrosion layers or tubercles/scale; and corrosion-
related sediment. These corrosion by-products in the bulk water, on the pipe walls
and deposited in the distribution system can accumulate organic sediments that
create a disinfectant demand and that act as a habitat and nutrients for
opportunistic pathogens. Low disinfectant residual due to a lack of corrosion
control can result in water quality changes and opportunistic pathogen growth.

•	Corrosion tubercles can also contain more coliform bacteria than finished water or
untreated source water.

•	When thick scales or biofilms occur, the bacteria near the pipe wall may fully
consume oxygen and may release corrosive products. This is called microbially-
induced corrosion (MIC). The bacteria can use sulfur compounds, nitrite, or iron or
metal oxides as their energy source instead of oxygen and release acids as a waste
product. The acid acts as the corrosive agent at the point of MIC.

Strategies for Finding Potentially Corrosive Microbial Growth
Monitor across distribution system for spatial differences:

•	Little to no dissolved oxygen compared to the treated water at the distribution
system entry point, while having total nitrate/nitrite increase or pH fluctuation.

•	Copper concentration higher in flowing sample than in treated water.

•	Conductivity much higher in distribution sample than in treated water.

Awareness of distribution system issues and indicators:

•	Areas of low water use or low velocity with little to no disinfectant residual.

•	Pipe replacements: iron pipe with tubercle scale and red outermost layer and
taste & odor complaints (e.g., earthy-muddy water, rotten egg or sulfur smell).

•	Blue water from copper corrosion.

•	Pipe replacements: blue green stains on copper piping.



Disclaimer: To the extent this document mentions or discusses statutory or regulatory authority; it does so for
information purposes only. It does not substitute for those statutes or regulations, and readers should consult the
statutes or regulations themselves to learn what they require. The mention of trade names for commercial products
does not represent or imply the approval of EPA.

Examples of Utility Actions

In an urban PWS in the northeast
United States, low chlorine residual
was found in pockets of the distribution
system due to seasonal, high
temperatures and low water use.
Unlined cast iron pipe in one of the
pockets had recurring chlorine residual
losses not resolved by seasonal low
velocity flushing. To resolve the issue,
the cast iron pipe was replaced with
ductile iron pipe and low velocity
flushing restored the disinfectant
residual above the required minimum.

An Air Force base found high copper
concentrations and low disinfectant
residual during monitoring in newly
constructed facilities, including a
daycare center. Flushing didn't resolve
the problem, so a corrosion control
plan using orthophosphate was
initiated. After a passivation period,
flushed samples showed consistent
disinfectant residual in the distribution
system and reduced copper levels
below the action level.


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Potential Strategies to Address Corrosion-Related Considerations

•	Effective corrosion control treatment can reduce chlorine demand from
corrosion products and help maintain adequate disinfectant residual.

Methods employed to limit corrosion within a pipe may include pH/alkalinity
adjustment or addition of corrosion inhibiting chemicals such as phosphates
and silicates. The optimal treatment strategy is based on system-specific
factors including water quality and pipe materials.

•	Preventive maintenance using high-velocity unidirectional scour flushing or
pigging originating at treatment and progressing through the distribution
system to problematic areas can remove sediment and scales.

•	Water main rehabilitation can remove corrosion tubercles and protect pipe
surfaces with liners. This restores the smooth interior pipe wall.

•	Under federal regulation 40 CFR 141.90(a)(3), before changing long-term
corrosion control or disinfection chemicals or source water, notify the
primacy agency and comply with regulatory requirements to assure
corrosion control remains optimized.

Disinfectant residuals should be kept at levels that will maintain
minimum disinfectant residual requirements, especially in areas having
difficulty maintaining them.

•	Additional benefits of a corrosion control plan are that it can extend the life of infrastructure; decrease metal release
and concentrations at the tap; reduce hydraulic issues from pipe scale build up and decrease pumping costs; diminish
aesthetic issues (e.g., color, taste, and odor); reduce infrastructure failures; and help to reduce biofilm growth.

•	For pipe installation or replacement in areas with corrosive or salty soils use poly-wrapped or poly-encased pipe.

Table 1. Resources and Guidelines related to Corrosion Control and Disinfectant Residual

Resource Title and URL

Relevance to Corrosion Control and Disinfectant Residual

AWWA Staff, (2017), What Are Some Best Practices for Internal

Corrosion Control? Opflow, 43(11), 8-9.

https://doi.org/10.5991/OPF.2017.43.0076

Note: There may be a fee associated with obtaining this resource.

Review of how to approach creating a corrosion control plan.

Lytie, D, A,, & Liggett, J, (2016). Impact of water quality on chlorine
demand of corroding copper. Water Research, 92,11-21,

https://doi.org/10.1016/i.watres,2016.01,032

Note: There may be a fee associated with obtaining this resource.

Evaluates how water chemistry shifts from the addition of pH
and orthophosphate impact corrosion and chlorine
concentrations.

Grace, S., Lytle, D. A,, & Goltz, M. N. (2012). Control of new copper
corrosion in high-alkalinity drinking water. JAWWA, 104(1), E15-E25,

https://doi. org/10.5942/iawwa. 2012.104.0002

Note: There may be a fee associated with obtaining this resource.

Highlights the interactions between new copper pipes, a
change in corrosion control, and the consumption of free
chlorine.

AWWA. (2017). M68 Manual of Water Supply Practices. Water Quality in

Distribution Systems, https://www.awwa.org/

Note: There may be a fee associated with obtaining this resource.

Describes factors affecting corrosion-related water quality.
Explains how to select an appropriate corrosion control
method and the role of corrosion in disinfectant residual
management.

Tang, M., Fields, R, E., Buse, H.Y., Lytle, D. A., Schock, M, R., Harmon, S.,
Kireta, A., and Triantafyllidou, S. (2021). How to Prevent Copper
Corrosion in Drinking Water Pipes, https://doi.org/10.1002/opfl.1574
Note: There may be a fee associated with obtaining this resource.

Describes copper corrosion-related water quality and
strategies for solving the blue water phenomenon.

Prest, E., Hammes, F., van Loosdrecht, M. C. M., & Vrouwenvelder, and
J. S, (2016). Biological Stability of Drinking Water: Controlling Factors,
Methods, and Challenges.

https://doi.org/10.3389/fmicb.2016.00045

Describes biological stability of drinking water including
descriptions of interactions between biofilm, sediment, and
bulk water. Also discusses advanced approaches for
assessment of biological stability.

Office of Water (4606)
EPA 815-F-22-013
August 2023

mm

Spot Flushing Application

Image Source: Confluence Engineering Group.
Used with permission.


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