Is Hot Water from an Instant Water Heater Enough to Kill Bacteria?

When it comes to personal hygiene and home water safety, many people think that hot water from an instant water heater is enough to kill bacteria. While this assumption is only partially true. In reality, the temperature of the water, how consistently it is heated, and how well the heater is designed to prevent bacterial growth all play a crucial role. For households that prioritize safety and long-term cleanliness, understanding these factors is key.

The Truth About Hot Water and Bacteria

Hot water does help kill bacteria, but it depends heavily on reaching the right temperature. According to the Occupational Safety and Health Administration (OSHA), water must reach at least 60°C (140°F) to effectively kill most harmful microorganisms, including Legionella bacteria. However, many instant water heaters are commonly set to lower temperatures—typically between 37°C and 45°C—for user comfort during showers and washing. These settings, while pleasant, are often not hot enough to eliminate bacteria.

Furthermore, bacteria can begin to grow in parts of the water system before the water even reaches its target temperature. Any residual or stagnant water in the inlet, outlet, or internal chambers of the heater can provide a warm, damp environment ideal for bacterial growth. This means relying solely on hot water without additional antibacterial features may still leave your water system exposed to contamination.

What is Legionella and Why Is It Dangerous?

One of the most dangerous bacteria associated with domestic water systems is Legionella. This microorganism thrives in water temperatures ranging from 20°C to 50°C (68°F to 122°F) and can cause Legionnaires’ disease, a severe and sometimes fatal form of pneumonia. The bacteria are most commonly spread through inhaling mist or vapor from contaminated water, making showers and faucets potential sources of exposure.

How the Royal Series by Rheem Stands Out

The Rheem Royal Series, which includes three models—Royal Platinum, Royal Plus, and Royal—has been engineered to provide peace of mind when it comes to water hygiene and safety. One of its standout features is its built-in AG+ (silver ion) antibacterial protection, integrated into the water inlet and outlet. Silver ions are known for their powerful antimicrobial properties and have been proven to kill 99.9% of bacteria on contact. This protection works 24/7, even when the heater is turned off, ensuring bacteria are neutralized from the moment water enters the system.

In addition to antibacterial defense, the Royal Series is equipped with a Replaceable Incoloy Heating Element. This heating element delivers fast and efficient heating while maintaining high, stable temperatures — a key factor in neutralizing heat-sensitive bacteria like Legionella. Its high resistance to scale and corrosion also means improved hygiene and a longer lifespan.

Finally, the Royal Series uses a Stainless-Steel Heating Chamber. Unlike plastic alternatives, stainless steel offers superior durability and a hygienic surface that resists bacterial build-up and is easier to clean. These features come together to provide a water heating experience that is not only reliable and efficient but also safe for you and your family.

Why Just Heat Isn’t Enough

 Heating water is a vital line of defense, but it’s not a complete solution. If water isn’t heated to a high enough temperature—or if bacteria are allowed to grow in stagnant areas before heating begins—you still face potential risks. That’s why the Rheem Royal Series goes further, combining thermal efficiency with built-in antibacterial protection to keep your water clean, safe, and reliable at all times.

Whether you choose the Royal Platinum, Royal Plus, or Royal model, you’re investing in a system designed to meet high standards of hygiene, performance, and long-term value. Find your nearest Rheem authorized dealer today.