NIST Receives New Patent for Microbe-Killing Water HeaterIt’s easy to take hot running water for granted. Simply twist a knob, and it comes po...
Published by Water Network Research, Official research team of The Water Network
NIST Receives New Patent for Microbe-Killing Water Heater
It’s easy to take hot running water for granted. Simply twist a knob, and it comes pouring out. But hot plumbing comes with a risk — the potential growth of harmful bacteria. Researchers at the National Institute of Standards and Technology (NIST) have just been granted a patent for a water heater system that kills a class of harmful bacteria, reducing the risk of Legionnaires’ disease and other life-threatening infections, while reducing the associated risk of scalding.
A side-by-side comparison of a typical water heater system and the new system invented at NIST. A heat exchanger allows the water tank to be safely heated to a higher temperature, killing certain bacteria such as Legionella. Credit: Brandon Hayes/NIST
Plumbing Has Changed
Residential plumbing has changed dramatically in the last few decades. Although there are more toilets, faucets, showers and appliances in the average modern home, those fixtures don’t use as much water as they used to. For example, many old showerheads sprayed more than five gallons of water per minute, while showerheads sold since the ’90s use less than half that amount. These changes reduce water bills, but the size of the pipes that supply those fixtures have not changed to match. More pipes and less flow means that water stays in a building’s pipes for longer. This warm water between your water heater and your shower (or any other outlet) creates ideal conditions for harmful bacteria such as Legionella pneumophila to grow.
Legionella Thrives in Warm Water
Legionella pneumophila lives naturally at low concentrations in many water sources such as rivers and soil. This bacterium thrives in warm water, so it can build up in plumbing systems. If water with a high concentration of Legionella pneumophila gets spread through the air in tiny droplets (aerosolized), it can enter your lungs and infect you with Legionnaires’ disease.
This illness — and the bacteria that cause it — was first discovered by the CDC in 1976 after a major outbreak at a convention for the American Legion, which is where the disease gets its name. It’s a severe type of pneumonia with a fatality rate of 10%. The elderly and immunocompromised are particularly vulnerable.
There are a little over 6,000 confirmed cases of Legionnaires’ disease in the U.S. per year. The real number could be 10 times higher or more because Legionnaires’ isn’t routinely tested for, but the disease is still relatively rare. “Code professionals and plumbing engineers work hard to prevent exposure that could result in outbreaks,” said Dave Yashar, the NIST mechanical engineer who invented the new water heater. “But it can be a complicated problem to keep in check, so we’ve come up with a way to do it more efficiently.”
The New Water Heater Design
Controlling water temperature throughout the entire plumbing system is the main way bacterial growth is kept at bay. Deciding what temperature a water heater should be set to is a delicate balancing act. If it’s too hot, the heater will use more energy and the water could burn residents. If it’s not hot enough, bacteria could become a problem.
Legionella pneumophila thrives in temperatures between 20 and 45 degrees Celsius (68-113 degrees Fahrenheit). Typically, water heaters are set to 49 C (120 F) in residential settings and slightly warmer in high-occupancy facilities. These temperatures in the hot water tank will slow bacterial growth and may kill some Legionella pneumophila, but not completely. Once the water leaves the heater and enters the building’s piping network, water in the pipes cools to the ideal temperature for Legionella, allowing surviving bacteria to multiply.
David Yashar’s patent describes a kind of water heater that can safely raise water to a much higher temperature of 70 C (160 F), hot enough to kill nearly all Legionella almost instantly. Some hearty heat-resistant microbes can survive at those temperatures, but they aren’t a major health concern. Then immediately after the water leaves the tank, a heat exchanger cools the outgoing water to a safe temperature before sending it off to faucets, showers and other house fixtures.
A heat exchanger is a device that transfers heat between two fluids without having them come in direct contact with each other. Imagine a long, twisty straw full of hot water passing through a box of cold water. The hot water cools down as it flows through the straw, and the cold water in the box heats up. The heat exchanger makes it possible to cool the water to a safe temperature without introducing live Legionella from any other supply.
SOURCE: https://www.technology.org/2026/08/22/nist-receives-new-patent-for-microbe-killing-water-heater/
It’s easy to take hot running water for granted. Simply twist a knob, and it comes pouring out. But hot plumbing comes with a risk — the potential growth of harmful bacteria. Researchers at the National Institute of Standards and Technology (NIST) have just been granted a patent for a water heater system that kills a class of harmful bacteria, reducing the risk of Legionnaires’ disease and other life-threatening infections, while reducing the associated risk of scalding.
A side-by-side comparison of a typical water heater system and the new system invented at NIST. A heat exchanger allows the water tank to be safely heated to a higher temperature, killing certain bacteria such as Legionella. Credit: Brandon Hayes/NIST
Plumbing Has Changed
Residential plumbing has changed dramatically in the last few decades. Although there are more toilets, faucets, showers and appliances in the average modern home, those fixtures don’t use as much water as they used to. For example, many old showerheads sprayed more than five gallons of water per minute, while showerheads sold since the ’90s use less than half that amount. These changes reduce water bills, but the size of the pipes that supply those fixtures have not changed to match. More pipes and less flow means that water stays in a building’s pipes for longer. This warm water between your water heater and your shower (or any other outlet) creates ideal conditions for harmful bacteria such as Legionella pneumophila to grow.
Legionella Thrives in Warm Water
Legionella pneumophila lives naturally at low concentrations in many water sources such as rivers and soil. This bacterium thrives in warm water, so it can build up in plumbing systems. If water with a high concentration of Legionella pneumophila gets spread through the air in tiny droplets (aerosolized), it can enter your lungs and infect you with Legionnaires’ disease.
This illness — and the bacteria that cause it — was first discovered by the CDC in 1976 after a major outbreak at a convention for the American Legion, which is where the disease gets its name. It’s a severe type of pneumonia with a fatality rate of 10%. The elderly and immunocompromised are particularly vulnerable.
There are a little over 6,000 confirmed cases of Legionnaires’ disease in the U.S. per year. The real number could be 10 times higher or more because Legionnaires’ isn’t routinely tested for, but the disease is still relatively rare. “Code professionals and plumbing engineers work hard to prevent exposure that could result in outbreaks,” said Dave Yashar, the NIST mechanical engineer who invented the new water heater. “But it can be a complicated problem to keep in check, so we’ve come up with a way to do it more efficiently.”
The New Water Heater Design
Controlling water temperature throughout the entire plumbing system is the main way bacterial growth is kept at bay. Deciding what temperature a water heater should be set to is a delicate balancing act. If it’s too hot, the heater will use more energy and the water could burn residents. If it’s not hot enough, bacteria could become a problem.
Legionella pneumophila thrives in temperatures between 20 and 45 degrees Celsius (68-113 degrees Fahrenheit). Typically, water heaters are set to 49 C (120 F) in residential settings and slightly warmer in high-occupancy facilities. These temperatures in the hot water tank will slow bacterial growth and may kill some Legionella pneumophila, but not completely. Once the water leaves the heater and enters the building’s piping network, water in the pipes cools to the ideal temperature for Legionella, allowing surviving bacteria to multiply.
David Yashar’s patent describes a kind of water heater that can safely raise water to a much higher temperature of 70 C (160 F), hot enough to kill nearly all Legionella almost instantly. Some hearty heat-resistant microbes can survive at those temperatures, but they aren’t a major health concern. Then immediately after the water leaves the tank, a heat exchanger cools the outgoing water to a safe temperature before sending it off to faucets, showers and other house fixtures.
A heat exchanger is a device that transfers heat between two fluids without having them come in direct contact with each other. Imagine a long, twisty straw full of hot water passing through a box of cold water. The hot water cools down as it flows through the straw, and the cold water in the box heats up. The heat exchanger makes it possible to cool the water to a safe temperature without introducing live Legionella from any other supply.
SOURCE: https://www.technology.org/2026/08/22/nist-receives-new-patent-for-microbe-killing-water-heater/
Tags
- Water & Diseases
- Water Supply
- Water Supply
- Water Risk
- waste water bacteria
- Domestic Water Use
- United States