Florida’s reputation for sun and water often includes an unpleasant sensory experience: unusual odors in both tap water and natural bodies of water. This is caused by two distinct problems rooted in the state’s unique subtropical climate and porous geology. Odors range from a sharp, “rotten egg” scent in drinking water to an earthy or fishy smell emanating from lakes and coasts. Understanding the source requires looking beneath the surface, where Florida’s vast underground aquifers and warm surface waters create conditions for odor-producing substances to thrive.
The Rotten Egg Odor: Florida’s Sulfur-Rich Groundwater
The distinct “rotten egg” smell often noticed in tap water, particularly from private wells or deep municipal sources, is the result of hydrogen sulfide gas (H₂S). This gas forms naturally deep underground within Florida’s vast limestone aquifer system. As water moves through the porous limestone, it reacts with organic matter and sulfur deposits trapped within the rock.
The breakdown of deeply buried organic material in these oxygen-deprived environments allows sulfate-reducing bacteria to flourish. These specialized microorganisms metabolize naturally occurring sulfates in the water, releasing H₂S as a byproduct. The smell can be detected by the human nose at extremely low concentrations. It becomes most noticeable when hot water is used, as the heat increases the vaporization of the gas.
While the H₂S odor is bothersome and makes water taste unpleasant, the gas is generally not considered a health concern at the low concentrations found in most residential supplies. However, its presence causes problems for homeowners because hydrogen sulfide is corrosive. This corrosion can lead to the premature failure of copper plumbing, fixtures, and water-using appliances. The gas also causes black staining on silverware and plumbing fixtures, indicating a need for water treatment.
Musty and Fishy Smells: The Role of Algae and Environmental Factors
A different set of odors—earthy, musty, or fishy—originates in Florida’s surface waters, including lakes, rivers, and coastal areas. These smells are primarily linked to the growth and decay of algae and cyanobacteria (blue-green algae). Cyanobacteria produce specific organic compounds that act as potent odorants.
Two common compounds responsible for the musty scent are geosmin and 2-methylisoborneol (MIB). These metabolites are released by certain species of cyanobacteria. The human nose is incredibly sensitive to them, detecting concentrations as low as 5 to 10 parts per trillion. Production of geosmin and MIB increases significantly during late summer and early fall, when warm water temperatures and high nutrient loads create ideal bloom conditions.
Florida’s coastal waters occasionally experience severe fishy or putrid odors caused by harmful algal blooms, such as Red Tide. Red Tide is caused by the marine organism Karenia brevis, which releases neurotoxins into the water and the air. These blooms lead to massive fish kills, and the subsequent decomposition of the dead fish and other marine life is what creates the overwhelming stench. The decaying organisms can also release H₂S into the air, adding a rotten egg smell to the environmental odor.
Testing, Treatment, and Safety Concerns
Homeowners dealing with the rotten egg odor in their tap water have several treatment options, often beginning with testing to confirm the H₂S concentration. If the smell is isolated to the hot water, the problem may be sulfur bacteria growing inside the water heater. Flushing the tank or replacing the magnesium anode rod can help resolve this specific issue.
For persistent H₂S throughout the water system, common solutions involve specialized filtration. These include aeration systems that physically vent the gas, or oxidizing filters that convert the gas into a removable solid. Chemical treatments like chlorination or the use of catalytic carbon filters are also effective at removing H₂S.
Addressing the musty or earthy odor caused by geosmin and MIB in municipal water supplies requires utility-scale treatment methods. These compounds are challenging to remove, but water treatment plants often utilize advanced processes. Examples include ozonation or the addition of powdered activated carbon to absorb the odorants. Individuals can sometimes mask the taste and odor by chilling the water or adding a slice of lemon.
While geosmin and MIB are not a public health concern, contact with water during severe cyanobacteria or Red Tide blooms can pose risks. Avoid swimming or letting pets enter water that is visibly discolored or contains algal mats. The toxins can cause skin irritation, respiratory issues, or gastrointestinal illness if swallowed or inhaled as aerosols. For any water quality concern, consulting municipal reports or performing a certified well water test is the most direct way to identify the cause and determine the appropriate action.