Contractors for Central Alabama Water (CAW) will conduct a dye test at Lake Purdy Dam Tuesday, November 4.
For Immediate Release: Monday, November 3, 2025
Contractors for Central Alabama Water (CAW) will conduct a dye test at Lake Purdy Dam Tuesday, November 4. The test is part of a larger project to strengthen the dam.
Passersby may notice some of the dye in the Little Cahaba River and possibly the Cahaba River for a brief period during and after the test. The dye is non-toxic, biodegradable and NSF approved. There is no risk to the river or to drinking water because water from the Cahaba River is filtered and treated at the Shades Mountain Filter Plant before it is distributed to customers.
“We don’t want the public to be alarmed if they see the dye in the water,” said Mac Underwood, General Manager of Central Alabama Water. “This test is necessary for engineers to gather information as we proceed with construction at the dam.”
Engineers are using the dye test to look for water seepage pathways between the upstream and downstream sides of a dam. Dye will be released in two locations upstream of the dam. Engineers will then take photos of the downstream area at regular intervals for three hours. They later analyze the results and provide a report to the CAW.
Construction is currently underway on Phase 1 of the project which involves installing roller compacted concrete as structural support to strengthen the dam. The cost of Phase 1 is $28 million.
About Lake Purdy Dam and Reservoir
Lake Purdy Dam and Reservoir are located in northern Shelby County. The original construction of the dam was completed in 1910. A project completed in 1929 raised the dam to its current height of 73 feet and length of 445 feet. The reservoir has a capacity of 5.6 billion gallons. It is a major drinking water source for a large portion of the CAW’s service area including Birmingham, Homewood, Hoover, Mountain Brook, Vestavia Hills and surrounding areas. Visit https://www.bwwb.org/lakepurdy for more information.
About Central Alabama Water
Central Alabama Water (CAW) serves customers in Jefferson, Shelby, St. Clair, Blount and Walker counties. The CAW operates four filtration plants, a certified testing laboratory and has more than 4,100 miles of water main in its distribution network. Visit www.bwwb.org for more information.
