Drinking Water Distribution System Tools and Resources
Drinking water distribution systems connect water treatment plants or water sources (in the absence of treatment) to customers via a network of pipes, storage facilities, valves, and pumps. In addition to providing water for domestic use, distribution systems may supply water for fire protection, agricultural, and commercial uses. Public water systems (PWSs) are responsible for operating and maintaining their distribution systems, which extend from the designated entry point to the distribution system (EPTDS) – typically the source or water treatment plant - up to the service connection, after which the piping is the property owner’s responsibility.
Distribution systems represent the vast majority of the physical infrastructure for water systems and serve as the final barrier against contamination. Distribution systems must be operated and maintained to reduce the risk of contamination from external sources or internal sources such as microbial growth or corrosion within the system.
EPA has developed many resources and tools related to distribution system water quality which have been collected on this page under the following categories or themes. These categories are not exhaustive, and many challenges may fall under multiple categories:
- Distribution System Evaluation
- Distribution System Research
- Microbial Growth, Biofilms and Sediments
- Disinfectants and Disinfection Byproducts
- Water Age
- Storage Facility Management
- Pressure Management
- Water Losses and Main Breaks
- Corrosion, Permeation, and Leaching
- Cross-Connections and Backflow
Distribution System Evaluation
Hydraulic modeling (EPANET)
EPANET is a software application for understanding the movement and fate of drinking water constituents within a drinking water distribution system. EPANET can be used to design and size new water infrastructure, retrofit existing aging infrastructure, optimize operations of tanks and pumps, reduce energy usage, investigate water quality problems, and prepare for emergencies.
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Use of Modeling to Protect Water Quality (pdf) (Distribution System Water Quality Fact Sheet)
Strategies for Evaluating Water Quality and Hazards
Distribution systems are large complex networks and water quality may change rapidly with system conditions, making it challenging to detect issues in real time. The following resources provide information on potential indicators of contamination, online water quality monitoring approaches and hazard analysis strategies.
- Protecting Water Quality with Online Water Quality Monitoring (pdf) (Distribution System Water Quality Fact Sheet)
- Distribution System Indicators of Drinking Water Quality (2006 TCR Issue Paper)
- Online Water Quality Monitoring Resources
- Hazard Analysis Critical Control Point (HACCP) Strategies for Distribution System Monitoring, Hazard Assessment and Control (2006 TCR Issue Paper)
Asset Management
Asset management is the practice of managing infrastructure capital assets to minimize the total cost of owning and operating them, while delivering high levels of service. This management framework has been widely adopted by the water sector as a means to pursue and achieve sustainable infrastructure. The following resources discuss infrastructure maintenance, rehabilitation, and replacement as key components of maintaining distribution system water quality and how the asset management framework can help systems prioritize and manage these activities.
- Asset Management Resources
- Distribution System Inventory, Integrity and Water Quality (2007 TCR Issue Paper)
Distribution System Research
EPA's Office of Research and Development conducts and funds research related to innovative solutions to drinking water issues, including those related to the distribution system. This research is especially focused on small systems, but many resources are also applicable to larger water systems.
The National Academy of Sciences Committee on Public Water Supply Distribution Systems and the Total Coliform Rule/Distribution System Advisory Committee (TCRDSAC) have each produced various reports and summaries related to distribution system risks, priorities, and research needs. These resources are collected together under the Distribution System Research and Information Collection Partnership (RICP).
Microbial Growth, Biofilms and Sediments
Under certain conditions, microbial organisms in the distribution system may grow and form biofilms. Some of these organisms may be opportunistic pathogens. Once biofilm development begins, material, organisms and contamination introduced to the distribution system can become entrained in the biofilm and accumulate or proliferate, resulting in more biofilm growth and potential release of these materials and organisms into the water. Biofilms and sediments can also reduce disinfectant residual levels and protect organisms from disinfection. The following resources describe health risks and other concerns related to microbial growth, biofilms, and sediment in distribution systems, as well as potential control measures.
- Protecting Water Quality with HPC Monitoring (pdf) (Distribution System Water Quality Fact Sheet)
- Protecting Water Quality with Pigging and Swabbing (pdf) (Distribution System Water Quality Fact Sheet)
- Protecting Water Quality Through Distribution System Flushing (pdf) (Distribution System Water Quality Fact Sheet)
- Health Risks From Microbial Growth and Biofilms in Drinking Water Distribution Systems (pdf)
- Effect of Treatment on Nutrient Availability (2007 TCR Issue Paper)
- Inorganic Contaminant Accumulation in Potable Water Distribution Systems (2007 TCR Issue Paper)
Disinfectants and Disinfection Byproducts
Under the Surface Water Treatment Rule, most drinking water systems that treat surface water (i.e., water from rivers, lakes, and streams) or groundwater under the direct influence of surface water are required to disinfect their water and maintain a disinfectant residual in their distribution system. Disinfection is required to reduce risks from microbial pathogens such as Giardia and Cryptosporidium which can cause severe gastrointestinal illness.
Disinfection byproducts (DBPs) can form in water when disinfectants combine with naturally occurring organic materials found in source water, in both the treatment process and later in the distribution system. Consuming water with levels of DBPs in excess of EPA’s standards over many years is associated with an increased risk of adverse health outcomes, including cancer. Under the Stage 1 and Stage 2 DBP Rules, PWSs that use chemical disinfection are required to limit exposure to DBPs in their finished drinking water.
The following resources describe water quality concerns related to disinfectants and DBPs in distribution systems, as well as potential measures used for balancing disinfection to reduce microbial risk while minimizing formation of DBPs.
- Maintaining a Disinfectant Residual (pdf) (Distribution System Water Quality Fact Sheet)
- Simultaneous compliance guidance manual for Stage 2 Rules (compliance with microbial and DBP rules)
- Simultaneous compliance workbook (complement to guidance manual)
- Approaches to prioritize distribution system optimization efforts (particularly DBPs): find information on this page related to optimizing disinfectant residuals and disinfection byproducts in your distribution system, including:
- Protocol for distribution system influent hold study: find information and tools on this page on how to conduct a distribution system influent hold study
- Web application for modeling chlorine breakpoint curves
- Web application for modeling chloramine formation and decay
- The Effectiveness of Disinfectant Residuals in the Distribution System (2007 TCR Issue Paper)
Nitrification
Distribution system nitrification is the formation of nitrate and nitrite from nitrogen compounds in the distribution system. It is an especially important issue for water utilities that use chloramines as a secondary disinfectant. Excess levels of nitrate or nitrite can cause severe health effects in infants and young children, including “blue baby syndrome”. The following resources describe water quality concerns related to nitrification in distribution systems, including increased residual degradation and microbial and biofilm growth as well as potential control measures.
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Protecting Distribution System Water Quality through Control of Nitrification (pdf) (Distribution System Water Quality Fact Sheet)
- Nitrification (pdf)
Water Age
Water age is the time water spends in the distribution system prior to use and can be indicative of the overall quality of delivered drinking water. As water ages, conditions may favor the growth of biofilm-related opportunistic pathogens and disinfection byproducts may increase while disinfectant residual levels may decrease, increasing the risk posed by some internal and external contaminants. The following resources describe water quality concerns related to water age in distribution systems as well as potential control measures such as distribution system optimization.
- Protecting Water Quality Through Water Age Management (pdf) (Distribution System Water Quality Fact Sheet)
- Approaches to prioritize distribution system optimization efforts (including strategies to reduce water age)
- Effects of Water Age on Distribution System Water Quality (pdf)
Storage Facility Management
Finished water storage facilities generally refer to tanks, standpipes, or reservoirs, used to store finished water that does not undergo further treatment. Finished water storage facilities are susceptible to sanitary risks including physical gaps (e.g., open access hatches, broken vent screens), contaminant sources (e.g., bird droppings on the tank roof), as well as sediment and biofilm buildup which could harbor opportunistic pathogens such as Legionella. The following resources describe water quality concerns related to finished water storage facilities as well as potential control measures such as inspection and cleaning.
- Protecting Water Quality Through Finished Water Storage Facility Inspection and Cleaning (pdf) (Distribution System Water Quality Fact Sheet)
- Drinking Water Storage Tank Assessment Protocol (2021)
- Finished Water Storage Facilities (pdf)
Pressure Management
Pressure monitoring and management is integral to proper drinking water distribution system operation. Pressure management involves maintaining adequate pressure throughout a distribution system, including both minimum and maximum pressures under varying demand conditions. The following resources describe pressure-related water quality concerns as well as potential control measures that may be helpful for sustaining high water quality, reducing main breaks and water losses, and improving energy efficiency.
- Protecting Water Quality Through Distribution System Pressure Management (pdf) (Distribution System Water Quality Fact Sheet)
- The Potential for Health Risks from Intrusion of Contaminants into the Distribution System from Pressure Transients (pdf)
Water Losses and Main Breaks
Water loss from distribution system leaks and main breaks can result in lost revenue for the water system, wasted resources, and water quality concerns. Reducing water loss involves identifying and repairing breaches in the distribution system which, in addition to being sources of lost water, represent potential entry points for contamination to the system. The following resources describe concerns related to water loss and main breaks, such as leaks in the distribution system, as well as potential control and mitigation measures.
- Control and Mitigation of Water Losses in Distribution Systems (2010 manual)
- New or Repaired Water Mains (pdf)
- Deteriorating Buried Infrastructure Management Challenges and Strategies (pdf)
Corrosion, Permeation and Leaching
Corrosion in water systems (electrochemical and microbial-based processes) involves the interaction between a metal surface such as pipe wall or solder and water. Corrosion of metal pipe materials can result in the release (or leaching) of metals, such as lead and copper, into the water supply. The following resources describe water quality concerns related to corrosion, permeation, and leaching, as well as potential control measures such as corrosion control treatment. For more information on corrosion control treatment requirements related the Lead and Copper Rule (LCR), please visit the rule page.
- Impact of Corrosion Control on Disinfectant Residual (pdf) (Distribution System Water Quality Fact Sheet)
- Optimal Corrosion Control Treatment Evaluation Technical Recommendations
- Permeation & Leaching (pdf)
Cross-Connections and Backflow
Cross-connections are defined as actual or potential connections between non-potable sources and potable water which could allow non-potable materials to enter premise plumbing or distribution systems through backflow. Backflow is any unwanted flow of used or non-potable water, or other substances from any domestic, industrial, or institutional piping system back into the potable water distribution system. When cross-connections are present and there is lower pressure in potable water distribution systems than in the non-potable source, contamination can enter the distribution system. The following resources describe water quality concerns related to cross-connections and backflow, as well as potential control measures that may be helpful for sustaining high water quality, such as use of cross-connection control and backflow prevention programs.
- Protecting Water Quality through Cross-Connection Control and Backflow Prevention (pdf) (Distribution System Water Quality Fact Sheet)
- Cross-Connection Control Manual (2003)
- Cross-Connection Control: A Best Practices Guide (2006)
- Potential Contamination Due to Cross-Connections and Backflow and the Associated Health Risks (pdf)