After weeks of adjusting treatment procedures at its water purification plant to address reports of water discoloration, the City of Round Rock is implementing new treatment measures at Lake Georgetown, the community’s primary water source.
The green tint some residents have noticed in tap water is the result of naturally occurring manganese after the devastating flooding in Central Texas in early July 2025. While the water remains safe to drink, Round Rock has been working to restore the water’s clarity and appearance through enhanced treatment processes that balance safety, quality and customer confidence.
This summer’s flooding event pushed significant amounts of naturally occurring manganese from the soil into Lake Georgetown. Under typical conditions, manganese settles at the bottom of the reservoir in a solid form, similar to fine sediment. In this form, it’s fairly easy to remove through the City’s regular water treatment process, which uses a substance called aluminum sulfate to bind particles together so they can be taken out during settling and filtering. However, the stirring effect of floodwaters entering Lake Georgetown allowed manganese to dissolve and become distributed throughout the lake.
While manganese in its solid state can be physically removed, soluble manganese must go through a chemical oxidation process to prevent it from reacting with steel pipes and precipitating out later in the distribution system, which produces a colored tint in tap water that some customers began to notice in the weeks after the floods.
It is important to note that manganese is classified as a “secondary constituent,” meaning that its impacts are aesthetic—affecting color, taste and/or odor—with no impact to health or safety under 0.3 milligrams per liter (mg/L). Testing in July and August showed manganese levels of approximately 0.2 mg/L at the lake intake, about four times higher than the Texas Commission on Environmental Quality (TCEQ)’s recommended threshold of 0.05 mg/L (which is the level that studies show discoloration can occur). Current testing shows that the City of Round Rock has been able to lower the level of manganese to 0.09 mg/L through its treatment process.
“Our number one priority is always water quality and safety,” said Michael Thane, Executive Director of Public Works. “Our staff works tirelessly to ensure that our water always remains safe to drink. The adjustments we are making now are focused on improving its appearance, because our customers deserve water that not only meets all safety standards but also looks and tastes the way they expect it to.”
On Wednesday, Aug. 26, the City’s Public Works Department began implementing a new strategy to further improve the aesthetics of the City’s drinking water. Sodium permanganate is now being injected directly at the lake intake, which provides eight hours of contact time before water reaches the City’s treatment plant. Additional chlorine is also temporarily being used earlier in the treatment process. Together, sodium permanganate and chlorine act as strong oxidizing agents, converting soluble manganese into insoluble forms before it can reach the distribution system.
Customers can expect to experience these changes in the next two to three days as the newly treated water is distributed throughout the community. Although officials anticipate improvement in the water’s color, customers may notice some change in the smell of the water due to the reaction of the sodium permanganate and manganese.
This manganese challenge is not unique to Round Rock, as neighboring utilities drawing from Lake Georgetown have reported facing similar conditions. Over time, as fresher water cycles into the reservoir and manganese levels naturally decline, the discoloration issue is expected to subside. Until then, Round Rock’s water system operators will continue to adapt treatment processes to balance aesthetic improvements while maintaining safe, high-quality drinking water. For more information and updates, customers may visit www.roundrocktexas.gov/waterquality.
