Your water heater is an essential part of daily life—delivering hot water for showers, laundry, and dishes. But what if it’s also harboring something harmful? If you’ve noticed foul-smelling water, especially a rotten egg odor, it could be a sign of bacteria growing inside your water heater. This raises an important question: can bacteria in a water heater actually make you sick? The answer is yes—under certain conditions, bacteria in your water heater can pose health risks, especially if left unaddressed.
What Kind of Bacteria Can Live in a Water Heater?
The most common bacteria associated with smelly water heaters is sulfate-reducing bacteria (SRB). These microbes thrive in warm, stagnant water and feed on naturally occurring sulfates, producing hydrogen sulfide gas as a byproduct. This is what gives off the familiar rotten egg smell.
In rare cases, another concern is Legionella bacteria, which can cause Legionnaires’ disease—a potentially serious respiratory infection. Legionella grows in water heaters that are kept at temperatures between 95°F and 115°F, especially in underused or improperly maintained systems.
Can You Get Sick From These Bacteria?
- Sulfate-reducing bacteria aren’t typically dangerous when used externally (such as for washing or bathing), but they’re a sign of poor water heater maintenance. While not usually harmful to healthy people, the hydrogen sulfide they produce can irritate the eyes and respiratory tract at high levels. In rare cases, people with respiratory conditions like asthma might experience discomfort.
- Legionella bacteria, on the other hand, are more concerning. When water containing Legionella is aerosolized (think of the mist from a hot shower) and inhaled, it can lead to Legionnaires’ disease. Symptoms include coughing, fever, chills, muscle aches, and shortness of breath. It can be particularly dangerous for the elderly, smokers, and those with compromised immune systems.
What Causes Bacteria to Grow in Water Heaters?
Several factors can contribute to bacterial growth in your water heater:
- Low water temperatures: Temperatures below 120°F allow bacteria to survive and multiply.
- Sediment buildup: Over time, minerals and debris settle at the bottom of your tank, creating a warm, stagnant environment ideal for bacteria.
- Inactive plumbing: If your water heater or pipes go unused for extended periods, bacteria have more opportunity to thrive.
- Old or corroded anode rod: The anode rod, which helps prevent tank corrosion, can also encourage SRB growth if it’s made from magnesium.
How to Prevent Bacterial Growth in Your Water Heater
The good news is that there are simple steps you can take to reduce or eliminate the risk of bacterial contamination in your water heater:
- Increase the Temperature: Setting your water heater to at least 130°F (while using proper scald prevention at faucets) can kill off most harmful bacteria, including Legionella.
- Flush the Tank Regularly: Flushing removes sediment and mineral buildup that encourages bacterial growth.
- Replace the Anode Rod: Switching to an aluminum-zinc alloy rod can discourage sulfur-producing bacteria.
- Install a Water Treatment System: Softening hard water or using filtration can reduce mineral content and bacterial food sources.
- Run Unused Fixtures Weekly: Keeping water moving through all parts of your plumbing system helps reduce bacterial stagnation.
When to Call a Professional
If you suspect bacteria in your water heater—especially if you notice foul odors or experience any related health symptoms—it’s important to contact a licensed plumber. A professional can inspect your water heater, flush the system, replace the anode rod, and recommend long-term solutions. If Legionella is suspected, water testing may be necessary.
Stay Safe and Informed
While not all bacteria in your water heater are harmful, some can pose health risks—especially if you ignore the signs. Regular maintenance and timely inspections go a long way in keeping your water safe and your plumbing system healthy. If your hot water smells strange or hasn’t been serviced in years, don’t take chances. Schedule an inspection with a qualified plumber and breathe easy knowing your water heater is in good hands.
