The test is part of a larger project to strengthen the dam.
For Immediate Release: Tuesday, November 4, 2025
Contractors for Central Alabama Water today conducted a dye test at Lake Purdy Dam. The test is part of a larger project to strengthen the dam.
The dye test was used by engineers to look for water seepage pathways between the upstream and downstream sides of a dam. For the Lake Purdy Dam test, Schnabel Engineering released dye in two locations upstream of the dam. Engineers then took photos of the downstream area at regular intervals for three hours. They will now analyze the results and provide a report to Central Alabama Water. The testing is estimated to cost approximately $10,000.00.
“This stage of the construction project gave us an opportunity to further analyze the dam,” said Mac Underwood, General Manager of Central Alabama Water. “Our team looks forward to reviewing the results of the dye test and using it to inform the construction process.”
Two colors of dye were used for the test. The dye is non-toxic, biodegradable and NSF approved. Passersby may have noticed some of the dye in the Little Cahaba River and possibly the Cahaba River for a brief period during and after the test. 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.
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.
