Waterborne Pathogens

Viral, Bacterial, and Parasitic Pathogens


A goal of drinking water and wastewater treatment is to reduce the numbers of viable organisms to acceptable levels, and to remove or inactivate all pathogens capable of causing human disease. Despite the remarkable success of water treatment and sanitation programs in improving public health, sporadic cases and point-source outbreaks of waterborne diseases continue to occur. Waterborne pathogens include the microorganisms Giardia, Cryptosporidium and Legionella.


Legionella pneumophila

Legionella is currently the leading cause of US waterborne disease outbreaks but is still believed to be under-reported. Legionella is different from typical waterborne pathogens in that the route of exposure is inhalation rather than ingestion.

The National Academy of Sciences convened an expert committee to review the state of the science related to the management of Legionella in water systems, formulate recommendations to improve management of Legionella contamination of water systems, and consequently better control Legionnaires’ disease in the United States.  The report was completed in August 2019 and is entitled Management of Legionella in Water Systems. In conjunction with this report, NAS also released interactive science-based guidance for facility managers

U.S. Centers for Disease Control recently distributed a new Legionella guide

Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings  features a checklist to help building owners and managers identify where Legionella could grow and spread in a building and ways to reduce the risk of contamination. 

Information on how events outside of buildings can lead to Legionella growth, such as construction, water main breaks and changes to municipal water quality is also included.

AWWA recommends that utilities familiarize themselves with the guide and share it with relevant customers.

AWWA Guidance on Building Return to Service - A Framework for Building Managers

Responding to Water Stagnation in Buildings with reduced or No Water Use: A Framework for Building Managers provides a decision-making framework for building managers to design responses to building water system stagnation.

This document provides information to address the immediate need to respond to stagnation. Building managers then can update or create water management programs. Second, this document provides some “how to” resources for building managers assessing their building plumbing systems after/during stagnation and deciding what level of actions are needed.

Technical Guidance
Responding to Water Stagnation in Buildings with Reduced or No Water Use

AWWA Manuals
M7 Problem Organisms in Water Identification and Treatment
M48 Waterborne Pathogens
M68 Water Quality in Distribution Systems

Opflow | JournalAWWA | AWWA Water Science

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International Symposium on Waterborne Pathogens

This symposium explores a waterborne pathogens in water including distribution systems and premise plumbing systems


Water Quality and Technology Conference

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AWWA Policy Statements

AWWA's policy statements are brief statements on protecting and improving water supply, water quality, management, and the interests of the public and the environment. They are written by consensus, subject to review and comment by AWWA committees, councils, and members. Because they represent AWWA's position on these matters, they are approved by the AWWA Executive Committee of the board of directors.

Technical Committee Engagement

AWWA members are recognized globally for their industry expertise and their generosity in sharing that expertise for a better world through better water. AWWA members participate in committee activities, developing conference programs, writing technical manuals, developing standards, creating educational content and contributing to AWWA publications. Committee members primarily interact through conference calls, emails, and face to face meetings at conferences and events. More information on volunteering for an AWWA committee.

The following committees are active in addressing issues about waterborne pathogens