Drinking Water Systems
Municipal Water Systems
- Description – Drinking water that is supplied through municipal systems comes from surface water (e.g., streams, rivers, lakes, reservoirs) and/or ground water. Drinking water distribution systems are made up of treatment facilities, storage tanks, and pipes that deliver safe water to the community. Municipal water systems are regulated by the Environmental Protection Agency (EPA), which requires testing for over 90 contaminants, including microorganisms, inorganic and organic chemicals, radionuclides, and disinfectants. Contamination of drinking water can occur through source water, water treatment failures, physical deficiencies (e.g. broken distribution system pipes), or changes in water quality due to building-specific factors. Municipal water systems use various methods of water treatment to provide safe drinking water for their communities. The most common steps in water treatment used by community water systems (mainly surface water treatment) include: coagulation and flocculation, sedimentation, filtration, and disinfection. (e.g., chlorine or chloramine).
- Detection – The EPA monitors water quality in different components of the system up to the meter. A challenge to consider would be the lack of public health detection abilities in these systems because there is no standard surveillance for low pressure events (e.g., main breaks, maintenance activities). Additionally, people in homes and buildings use water in different ways (i.e., some communities choose to not drink tap water). These factors make it difficult to detect an outbreak.
- Investigation – Public health departments should partner with the water engineers and operators of these municipal systems as well as their state drinking water administrators (who could be within the health department or within separate agencies such as departments of environmental protection, etc.) to adequately investigate.
- Control – Common control methods include boil water advisories, do not drink advisories, do not use advisories, fire hydrant flushing, recommendations for homes/buildings to flush, and chlorine burns. Other solutions include maintenance, replacing, or repairing the water distribution system.
Outbreak Example: Giardia duodenalis, Utah 2012
Twenty-eight individuals who lived on the same street in the same neighborhood reported gastrointestinal illness within a 7-week period. Stool samples from five individuals were positive for G. duodenalis. In the month prior to the first case illness onset, the neighborhood’s municipal water distribution system transitioned from one municipal water system to another, which likely caused low pressure in the neighborhood’s section of the municipal water distribution system. The change in water pressure temporarily allowed non-potable water to flow into the water distribution system. The source of non-potable water was a previously unknown cross-connection between the neighborhood’s section of the municipal water system and a secondary irrigation water system. The cross-connection was fixed, and no additional illnesses were reported.
Image depicting a drinking water system. The path water takes from water source, to water treatment, to water distribution system
- Description – Private wells use ground water as their water source. Groundwater can become contaminated through naturally occurring chemicals and minerals (e.g. arsenic, radon), local land use practices (e.g. pesticides, chemicals, animal feeding operations), malfunctioning wastewater treatment systems (e.g. septic tanks), and other sources. Contamination of a private well can impact not only the household served by the well, but also nearby households using the same aquifer.
- Detection – The private well owner is responsible for the water safety and should regularly (e.g., annually) have well water tested for contaminants. The state health department may assist with testing the private well or direct the well owner to testing resources.
- Investigation – A well assessment and septic assessment conducted by certified professionals would be necessary to investigate or confirm the source of a private well outbreak.
- Control – If the source of the contamination is known, remediation of the current well and/or septic system is necessary to prevent ongoing contamination BEFORE initiating temporary water disinfection of the well. Alternative sources of water (e.g., new well, bulk water delivery) and/or wastewater removal/treatment (e.g., new septic system, portable toilets) may be necessary. Additionally, household water treatment systems can be considered. Visit CDC’s pages Choosing Home Water Filters & Other Water Treatment Systems and A Guide to Drinking Water Treatment Technologies for Household Use.