National Sanitation Foundation Water Quality Index
In 1970, the National Sanitation Foundation developed the Water Quality Index (NSFWQI), a standardized
method for comparing the water quality of various water bodies. The National Sanitation Foundation Water Quality Index (NSFWQI) is the most respected and utilized water quality index in the U.S. However, this index has been criticized for not adequately representing water quality in all areas of the U.S. The “one size fits all” structure of the index causes some regional water quality concerns to be overlooked in the overall index value.
In Iowa, the WQI is calculated by using eight
common water quality parameters (dissolved oxygen, fecal coliform bacteria, pH, 5-day BOD, total phosphorus,
nitrate-nitrogen, turbidity, and total dissolved solids). Values range from 0 – 100 and streams are classified as poor
(0-25), fair (25-50), medium (50-70), good (70-90), or excellent (90-100). WQIs were calculated on the streams
monitored monthly as part of Iowa’s Ambient Water Monitoring Program. For 2000-2005, 81% of the streams had a
WQI in the medium category while the remaining 19% were in the good category.
Streams in Iowa show seasonal WQI patterns. For the majority of streams, water quality is medium during the
spring, followed by a decline in water quality during the summer months when even more streams fall from the
good category into the medium and fair categories. During the fall, nearly half the streams exhibit medium
water quality while the rest have good water quality. Water quality is at its best during the winter months, with
nearly 69% of the streams classified as good.
Each colored marker on the map below represents a stream site that is monitored in our ambient site network. Follow the legend at the bottom right of the map to interpret the water quality rank of each marker (stream site).
When a marker is clicked, a small window appears revealing detailed information about the site.
Move your mouse over a marker on the map. Click to retrieve detailed site information. Use the Zoom and Pan buttons in the upper left corner of the map (or your mouse wheel) to view a site more closely. Use the View buttons (Map, Satellite, Hybrid, Terrain) in the upper right corner of the map to change your background data layers.