About Public Drinking Water Data
Tracking Public Drinking Water Quality involves collecting data about the levels of 10 select contaminants that are tested for in public drinking water supplies according to the Safe Drinking Water Act.
This page provides general information about drinking water quality data and measures developed by the Iowa Public Health Tracking program. Contact Us for more information about these data.
Information on this page:
What do these data tell us?
- The annual mean (average) and maximum concentrations of ,
- , di(2-ethylhexyl) phthalate (), disinfection byproducts (), , , tetrachloroethene (), trichloroethene (), and for community water systems in Iowa.
- If the concentrations of arsenic, atrazine, DEHP, DBP’s, nitrates, radium, PCE, TCE, and uranium are increasing or decreasing over time.
Back to top
How can we use these data?
- The data provides summary information on arsenic, atrazine, di(2-ethylhexyl) phthalate (DEHP), disinfection byproducts (DBPs), nitrates, radium, tetrachloroethene (PCE), tricloroethene (TCE), and uranium concentrations in drinking water from community water systems.
- These data can be used to determine the potential for public health impacts from contaminant levels of concern, they are not gathered specifically to assess the level of exposure or to track changes in water quality over time.
- State and local partners can use the data for program planning and evaluation.
- Several measures use comparisons to commonly-used benchmarks, such as the Maximum Contaminant Level (MCL). MCLs are developed to account for possible health risks, as well as how practical it is to treat water so that the contaminant concentration is lowered.
Back to top
What can these data not tell us?
- The sources of exposure for contaminants in drinking water.
- The levels of arsenic, atrazine, di(2-ethylhexyl) phthalate (DEHP), disinfection byproducts (DBPs), nitrates, radium, tetrachloroethene (PCE), tricloroethene (TCE), and uranium, in individual community water systems.
- Information about water quality in water sources other than community water systems and private wells.
- These data are not gathered specifically to assess the level of exposure or to track changes in water quality over time, they can be used to determine the potential for public health impacts from contaminant levels of concern.
Back to top
What are the sources of the data?
- The Safe Drinking Water Information System (SDWIS) which is maintained by the Water Supply Operations program at the Iowa Department of Natural Resources.
- requires community water systems to provide drinking water that meets standards established under the Safe Drinking Water Act.
Back to top
What time period of data is available?
- The Iowa Public Health Tracking portal displays public drinking water data from the year 2000 through the most recent year of data available.
Back to top
Why are the data limited to 10 select contaminants?
Back to top
How were non-detects handled in the data set?
- Sample results with concentrations less than the detection limit have been replaced with a value equal to 1/2 the detection limit for the analytical method used when calculating average concentrations.
- If all sample results during a time period were non-detects no average concentration is calculated and the is reported as a "ND".
- No sensitivity analyses were conducted to characterize how the approaches to handling non-detects may impact the drinking water quality data; therefore, it is possible that the analysis may produce biased estimates of the mean - especially if a large proportion of samples are below the limit of detection for the analytical method.
Back to top
What are the limitations of the data?
- These data are limited to community water systems in Iowa (i.e., systems that serve 15 or more locations or 25 or more people, year-round in Iowa.
- Does not include data on unregulated drinking water providers, namely private drinking water wells or very small systems or mutual in which there are less than 15 retail connections and less than 25 year-round residents.
- Concentrations in drinking water systems cannot be directly linked to exposures and health risks, because they do not account for water use and consumption practices. In addition, people may obtain drinking water from sources other than community water systems (e.g., private wells, bottled water, workplace, school). Concentrations may not reflect levels in finished drinking water or water at the consumer's tap.
- The current form of the data and measures contain one record for each active community water system per year (i.e., active at the time of data analysis). Sampling results from inactive systems that were active prior to data analysis are not included in the data and measures. Early missing values may be because the water system was not yet active, or the system was not required to take a compliance sample during that particular time period. The data set does not distinguish between these two scenarios.
- Trends can be difficult to interpret if water quality standards and treatment requirements change over time.
- Presenting average concentrations by calendar year is not usually consistent with how maximum contaminant levels () established by US Environmental Protection Agency (EPA) are calculated (i.e., typically based on running averages).
- The accuracy of the population served information is unknown. Water systems derive population estimates using census estimates, number of water connections, or other means during the year reported.
- Systems may receive a sampling waiver from the state for reduced frequency of monitoring based on low analytical results. Reduced monitoring frequencies lead to a reduced number of samples.
Back to top
Where can I find more technical information about the data?
More detailed documentation of the public drinking water data can be found in the following documents:
Indicator Profiles
Public Water Use 
Arsenic Contaminant Levels
DEHP Contaminant Levels
Haloacetic Acids and Trihalomethanes Contaminant Levels
Nitrate Contaminant Levels
PCE Contaminant Levels
Radium Contaminant Levels
TCE Contaminant Levels
Uranium Contaminant Levels
Descriptive Metadata
Public Drinking Water Facilities Inventory
Public Drinking Water Quality Sample Results
Contact Us to learn more about public drinking water data, or any of the measures displayed on the Iowa Public Health Tracking Portal.
Back to top