Everything Ohioans Need to Know About Cincinnati Water Quality

Where Does Cincinnati’s Tap Water Come From?

Cincinnati’s tap water comes from multiple sources, including both surface water and groundwater. It’s distributed by the Greater Cincinnati Water Works (GCWW), which supplies up to 43 billion gallons of water per year to 1.1 million consumers.

According to the 2023 Drinking Water Quality Report, around 88% of its source water comes from the Ohio River and is treated at the Richard Miller Treatment Plant.

Around 12% comes from 13 wells drawing water from the Great Miami Buried Valley Aquifer (GMBVA), which is treated at the Charles M. Bolton Treatment Plant.

Together, these water treatment plants produce an average of 132 million gallons of water per day, with daily water testing to ensure high-quality water supplies.

How Clean Are Cincinnati’s Water Sources?

The Great Miami Buried Valley Aquifer is located 30 feet to 300 feet beneath the cities of Fairfield and Hamilton. Although the sand and gravel in the aquifer acts as a natural filter, the aquifer is replenished by surface water, and the Ohio EPA considers it “highly susceptible to contamination due to the lack of an overlaying protective clay layer.”

The Ohio River is also “highly susceptible to contamination,” including from viruses and bacteria like cryptosporidium, mineral deposits, and agricultural runoff. It’s also at risk of contamination from forever chemicals (PFAS) and other industrial contaminants.

What Steps Is Cincinnati Taking to Protect Its Water?

One of the most important steps that Cincinnati is taking to protect its water supply is by monitoring the Ohio River for oil spills and other types of contamination. The Ohio River Valley Water Sanitation Commission (ORSANCO) is a multi-state organization that has 17 stations located along the Ohio River, from Paducah, KY, to Pittsburgh, PA.

Cincinnati has also participated in the Greater Cincinnati Water Works Case Study with the U.S. EPA to evaluate the physical security of its water system.

Additionally, the Greater Miami Buried Valley Aquifer is a Sole Source Aquifer, which means that any projects in the area must be “designed and constructed in a manner that does not create a significant hazard to public health.”

How Is Cincinnati’s Drinking Water Treated?

Like other American water systems, Cincinnati’s water supply goes through a multi-step treatment process before it enters the distribution system. This includes:

• Coagulation, flocculation, and sedimentation: Chemical coagulants are used to cause small pollutants to stick together and settle to the bottom of the tank.
• Filtration: Cincinnati uses rapid sand filtration, granular activated carbon, and a GAC reactivation furnace to physically filter out contaminants.
• Disinfection: GCWW uses ultraviolet light to kill viruses and bacteria, as well as chemical disinfectants like chlorine.
• Corrosion control: GCWW adjusts the pH levels to reduce the amount of lead that leaches out of pipes in the distribution system.
• Fluoridation: Cincinnati adds fluoride to the water to prevent tooth decay.

Water from the aquifer goes through a slightly less complex treatment process. GCWW adds lime as a natural water softener, and uses a coal and sand water filter instead of activated carbon. It also adds chlorine and fluoride during the treatment process.

Is Cincinnati’s Tap Water Hard or Soft?

Hardness refers to the amount of minerals like calcium and magnesium. Cincinnati’s tap water averages 127 milligrams per liter (mg/L) and 133 mg/L at its two treatment plants. This is considered relatively hard water, and Cincinnati residents may want to install a water softener to reduce scale buildup and improve the taste of the water.

Cincinnati’s tap water may also be cloudy, especially in the winter, due to the presence of dissolved oxygen. Neither of these issues present a health risk to consumers.

What Contaminants Are Found in Cincinnati’s Water Supply?

Cincinnati’s water quality meets the standards of the National Primary Drinking Water Regulations (EPA.gov). But the treatment process itself can leave behind disinfection byproducts, and other unwanted contaminants may remain.

The Environmental Working Group (EWG) found 13 contaminants that exceed their public health recommendations. These include:

Chromium-6 (Hexavalent)

Hexavalent chromium (chromium-6) is a chemical pollutant that contributes to several serious health problems, including cancer. In fact, it’s the chemical that Erin Brockovich brought to the world’s attention in the 1990s in Hinkley, CA.

The EPA hasn’t set a legal limit for it, but several public health bodies recommend an upper limit of 0.02 parts per billion (ppb).

Cincinnati’s tap water exceeds this recommendation by 5.9 times:

•  EPA maximum allowance: No legal limit
• EWG recommended maximum: 0.02 ppb
• Cincinnati maximum contaminant level: 0.117 ppb

Haloacetic Acids (HAA5)

Haloacetic acids are a group of disinfection byproducts, which means they’re not found in the source water but are formed during the water treatment process. At large doses, these acids are linked to cancer and harm to fetal development.

The EPA has set a maximum allowance of 60 ppb for five haloacetic acids (HAA5), but the EWG recommends a lower limit, which Cincinnati exceeds by 88 times:

• EPA maximum allowance: 60 ppb
• EWG recommended maximum: 0.1 ppb
• Cincinnati maximum contaminant level: 8.83 ppb

Haloacetic Acids (HAA9)

There are four more haloacetic acids that make up the HAA9 grouping. Unlike the HAA5 group, there’s no legal limit for these disinfection byproducts, but the EWG recommends no more than 0.06 ppb. Cincinnati’s HAA9 levels are 193 times higher:

• EPA maximum allowance: No legal limit
• EWG recommended maximum: 0.06 ppb
• Cincinnati maximum contaminant level: 11.6 ppb

Nitrate and Nitrite

Nitrate and nitrite levels may be elevated in areas where the source water is exposed to urban and agricultural runoff. At high levels, these chemicals can contribute to cancer, harm to fetal growth, and methemoglobinemia (blue baby syndrome).

Although Cincinnati’s nitrate and nitrite levels are within the EPA’s guideline of 10 parts per million (ppm), they exceed the EWG’s recommendation by 6.3 times:

• EPA maximum allowance: 10 ppm
• EWG recommended maximum: 0.14 ppm
• Cincinnati maximum contaminant level: 0.885 ppm

Total Trihalomethanes (TTHMs)

Trihalomethanes are a category of chemicals that arise during the disinfection process. They include chloroform, bromoform, and other chemicals that are harmful to health.

The EWG recommends that total trihalomethane levels to be below 0.15 ppb, but Cincinnati's TTHM levels are 252 times higher:

• EPA maximum allowance: 80 ppb
• EWG recommended maximum: 0.15 ppb
• Cincinnati maximum contaminant level: 37.9 ppb

Do Water Filters Improve Cincinnati Water Quality?

Cincinnati’s drinking water is already filtered and treated, so should you filter it again at home? There are definitely benefits to using a home water filtration system, including removing the disinfection byproducts that remain after the treatment process.

Activated carbon filters can remove many of these contaminants and improve the taste and smell of your water, while reverse osmosis filters are more effective at removing certain categories of contaminants, such as lead and forever chemicals (PFAS).

Check the NSF rating for your water filter to make sure that it’s certified to filter out the contaminants you want to remove.

Does Cincinnati’s Drinking Water Contain PFAS?

Per- and poly-fluoroalkyl substances (PFAS) are a growing concern for water utilities in the U.S. These “forever chemicals” are linked to a range of serious health effects, and are difficult to remove from the environment once they’ve been released.

Like many other American cities, forever chemicals have been detected in Cincinnati’s water supply. But according to the Cincinnati Enquirer, the city is “better off” than other nearby drinking water systems due to its advanced water treatment process.

GCWW’s water treatment process at the Richard Miller Treatment Plant uses a granular activated carbon (GAC) reactivation furnace that can reduce PFAS levels significantly. The Charles M. Bolton Treatment Plant, however, doesn’t use this technology, which may mean water from this plant has higher PFAS levels.

Is There Lead in Cincinnati’s Drinking Water?

Cincinnati’s drinking water doesn’t contain lead when it leaves the treatment plant, but it may pick up lead as it moves through the distribution system. This is more likely if your home is old and has a lead water main or service line.

According to MyGCWW.org, Cincinnati has replaced more than 15,000 lead service lines (or confirmed that they are not lead), but it still has over 35,000 to go.

If you want to check the lead levels at your home, you can request a free test kit from GCWW, or contact them at 513-651-LEAD.