Most homeowners in Marietta, East Cobb, Sandy Springs, and Smyrna are aware that their water tastes fine and passes every safety test. What fewer homeowners know is that the Cobb County-Marietta Water Authority’s water supply has a documented and researched interaction with copper plumbing that has been studied at the university level — and that understanding your specific water chemistry is the most useful thing you can do to protect your home’s plumbing and appliances over the long term.

This guide explains what is actually in Cobb County’s water based on the most recent official data, how it affects different components of your home’s plumbing system, and what treatment options are available.

Where Cobb County’s Water Comes From

The Cobb County Water System purchases treated water wholesale from the Cobb County-Marietta Water Authority, which operates two surface water treatment facilities. The Quarles Water Treatment Plant draws from the Chattahoochee River in east Cobb County. The Wyckoff Water Treatment Plant draws from Lake Allatoona, a Corps of Engineers reservoir in north Cobb County. Treated water from both plants is distributed throughout Cobb County’s 3,100-plus miles of water piping to homes and businesses in Marietta, East Cobb, Smyrna, Vinings, and surrounding communities.

The 2024 Cobb County Water Quality Report confirmed no EPA Safe Drinking Water Act violations. The water is safe to drink and meets all federal and state standards. The water quality concerns relevant to homeowners are not safety issues — they are about specific chemical characteristics of the treated water and how they interact with your home’s plumbing and appliances over time.

Cobb County Water Is Soft — The Corrosion Issue Is About Chemistry, Not Hardness

An important clarification that surprises many Cobb County homeowners: the CCMWA’s water supply is not hard water. Both Lake Allatoona and the Chattahoochee River are relatively low-mineral surface water sources. The Cobb County Water System’s 2024 test results show copper at the 90th percentile of just 0.054 ppm — well within EPA limits — and the water does not carry the high calcium and magnesium content associated with true hard water markets. The scale buildup that hard water produces is not the primary concern here.

The copper pipe corrosion problem that Cobb County is known for is driven by disinfection chemistry, not mineral hardness. This distinction matters because the right treatment approach is different.

The Copper Pipe Corrosion Connection — What the Research Shows

Pitting corrosion is a localized form of corrosion that creates small pits or holes in a metal surface — in this case, the interior wall of a copper supply pipe. Unlike uniform corrosion that thins the pipe wall evenly, pitting corrosion concentrates at discrete points and eventually penetrates the full wall thickness, producing the pinhole leaks that are one of the defining plumbing patterns in Cobb County’s pre-2000 housing stock.

The mechanism is driven by chloramines used in the CCMWA’s disinfection process. Chloramines — a combination of chlorine and ammonia — are more stable than free chlorine and maintain residual disinfection throughout the distribution system. But chloramines also interact with the protective copper oxide layer that forms on the interior of copper pipes, disrupting that layer and exposing the underlying metal to accelerated oxidation. This phenomenon was studied specifically in Cobb County in collaboration with Virginia Tech, and the findings confirmed what plumbers in this area have observed for decades: the chloramine-based disinfection chemistry is a primary driver of the area’s elevated pinhole leak rate in aging copper plumbing.

For homeowners in Marietta, East Cobb, and Sandy Springs with homes built before 2000 on original copper plumbing, this is the reason multiple pinhole leaks in different locations is a recurring pattern rather than isolated bad luck. Carbon filtration that reduces chloramine content can slow further pipe wall degradation, though it does not repair existing damage.

PFAS in Cobb County’s Water Supply

The Cobb County Water System’s 2024 report detected several PFAS compounds in monitoring conducted at both the Wyckoff and Quarles treatment plants. PFAS — per and polyfluoroalkyl substances, sometimes called “forever chemicals” — are a class of human-made compounds found in a wide range of consumer products and industrial processes. The specific compounds detected included PFOA (3.1 ppt), PFOS (2.7 ppt), PFBS (3.9 ppt), PFBA (4.4 ppt), PFPeA (4.4 ppt), and PFHxA (4.9 ppt). All were detected below EPA Maximum Contaminant Levels, meaning the water is in full compliance with federal standards.

PFAS are present at trace levels in many municipal water systems nationally due to their widespread use and environmental persistence. For homeowners who want to minimize PFAS exposure at the tap, a reverse osmosis system is the most effective residential treatment option — RO membranes remove PFAS compounds to levels below detection in most cases.

How Cobb County Water Affects Your Plumbing and Appliances

Water Heaters and Tankless Systems

While Cobb County’s water is not hard in the traditional sense, sediment and biofilm accumulation in water heater tanks still occurs over time and warrants annual maintenance flushing. For tankless water heater owners, annual descaling of the heat exchanger remains manufacturer-specified required maintenance. Navien and most other manufacturers require annual service, and the chloramine chemistry in CCMWA’s water is a reason to follow this schedule consistently rather than skipping years.

Fixtures, Aerators, and Taste

Some Cobb County homeowners notice a chloramine taste or smell in their water, particularly when chloramine treatment levels are higher during certain seasons. Aerator clogging can also occur from biofilm or particulates rather than scale. A whole-home carbon filter addresses both of these issues effectively, removing chloramines and improving taste and odor at every tap without changing the water’s soft, low-mineral character.

Water Treatment Options for Cobb County Homes

Whole-Home Carbon Filtration

Carbon filtration is the most directly relevant treatment option for most Cobb County homeowners. A whole-home carbon filter removes chloramines, chlorination byproducts, and organic compounds at the point of entry, addressing both taste and odor concerns and reducing one of the contributing factors in the documented copper pipe corrosion pattern. This is not a hard water solution — it is a disinfection chemistry solution, which is the appropriate response to Cobb County’s actual water quality profile.

Point-of-Use Reverse Osmosis

For drinking and cooking water quality, an RO system under the kitchen sink provides the highest level of residential filtration available. RO removes chloramines, disinfection byproducts, PFAS compounds, heavy metals, and most other regulated and unregulated contaminants. Given the PFAS detection levels reported in Cobb County’s 2024 water quality data, an RO system is a well-justified investment for homeowners concerned about long-term PFAS exposure from drinking water specifically.

Whole-Home Water Softeners

Because Cobb County’s water is already soft, a traditional water softener is not the primary recommendation for most homes in this area. Softeners address calcium and magnesium hardness — which is not Cobb County’s issue. Installing a softener on already-soft water adds unnecessary sodium to the supply and provides little benefit. A water quality assessment can confirm whether softening makes sense in any specific situation.

We are a Brita PRO authorized dealer and install and service whole-home carbon filtration systems, point-of-use RO systems, and water softeners throughout Marietta, East Cobb, Sandy Springs, Smyrna, and Vinings. A water quality assessment at your home can identify the specific treatment approach that addresses your situation most effectively.

Benjamin Franklin Plumbing® of Marietta serves homeowners throughout Marietta, East Cobb, Sandy Springs, Smyrna, Vinings, and Cumberland. Available 24/7 — call (770) 999-9871 or book online. Licensed, background-checked, and drug-tested technicians.