Expert Commentary

Hot tap water injures thousands of people in the US annually. An inexpensive device can help prevent these burns

Thermostatic mixing valves, which mix hot and cold water to deliver a specific temperature water to the tap, can prevent scald burns, but many older homes don't have them.

hot water
(Benjamin Nelan from Pixabay)

Burns from hot tap water caused at least 60,000 injuries and 110 deaths in the U.S. between 2016 and 2018 and resulted in more than $70 million in hospital costs each year, according to a recent study, which recommends a simple device to help prevent the problem.

The cost burden of hospital-treated tap water scald burns in the United States,” published in Injury Prevention in March, is one of the few to estimate the nationwide cost of tap water scald burns. Tap water scald burns involve faucets, bath, shower or sink water, as opposed to other types of scald burns, which involve hot water from other sources such as cookware.

The authors recommend thermostatic mixing valves, which can be installed in water heaters or at tap and shower fixtures, as an effective solution to reduce the risk of tap water scald burns. Also called anti-scalding valves, the devices automatically mix hot and cold water to deliver a desired temperature. They are relatively inexpensive, costing as little as $30, and can be installed by a qualified plumber.

“There’s a lack of awareness about this,” says Wendy Shields, the study’s lead author and senior scientist at Johns Hopkins Center for Injury Research and Policy. “You might not think this is a risk, but this is how many people are hurt and we have a device to prevent this from happening.”

The study

Each year, an estimated 486,000 people in the U.S. are treated for burns. Scald burns, which are caused by contact with hot water, make up about a third of all burns in the U.S., according to the American Burn Association. Scald burns are most common in children under 5. Older adults and people with disabilities are also at a higher risk.

Parsing out different types of scald burns, including tap water, at a nationwide scale became more feasible for researchers in 2015, when the U.S. adopted newer version of the international disease classification codes, known as ICD-10, published by the World Health Organization. ICD-10 has several injury codes involving hot tap water, including contact with hot tap water, scalds from bath or tub, and running hot water.

Shields and her co-authors, Joseph Levy, Linda Chyr and Shannon Frattaroli, used 2016 to 2018 data from the federal Healthcare Cost Utilization Project, the nation’s most comprehensive source of hospital care data, and collected the data on hot tap water injuries.

The study was funded by a grant to Johns Hopkins Bloomberg School of Public Health from the Centers for Diseases Control and Prevention. The authors reported no conflicts of interest.

Among their findings:

  • Between 2016 and 2018, 52,088 people in the U.S. visited emergency departments for tap water scald burns. An additional 7,270 were hospitalized and 110 died at the hospital.
  • In total, the cost of visits added up to $29.79 million for emergency department visits and $206.69 million for hospital stays.
  • Among those who were hospitalized, 41% were white, 28% were Black and 17% were Hispanic. About 9% were listed as “others” and data was missing for 5%. Race data were not available for emergency department visits.

Also, Medicaid and Medicare paid for 67% of inpatient stays and 47% of emergency department visits, reflecting that scald burns disproportionally affect older adults and lower-income populations. Medicaid covers people whose income is below a certain government threshold, while Medicare covers people who are 65 and older, regardless of income. Both programs cover people who have disabilities.

“We’re all paying these costs with federal dollars, and it has a simple engineering solution,” says Shields.

She adds it’s likely more people get scald burns than the study’s estimates show, because some might go to urgent care instead or not seek care at all. Also, the estimated costs exclude follow-up care costs, such as rehabilitation, medication, and infection treatment and control and do not account for societal costs, such as burdens on caregivers, pain and suffering and other costs.

Scald burns and thermostatic mixing valves

The severity of hot tap water scald burns depends on the water temperature, the duration of exposure and age of the person, Shields explains. For a child, 120 degrees Fahrenheit water will result in serious burns in 9 minutes, whereas 130 F water will cause serious burn in 25 seconds and 140 F water in as little as 3 seconds.

In 1988, water heater manufacturers voluntarily agreed with the Consumer Product Safety Commission to preset all new water heaters to 120 F. The federal agreement followed two states passing laws to require water heaters to be preset to 120 degrees, Washington in 1983 and Wisconsin in 1987.

“So, the reason we recommend it to be 120 degrees is to give people the time to get out of the way,” says Shields.

This agreement did not involve thermostatic mixing valves. Also, consumers can manually change the water heater settings. And soon researchers realized that scald burns were still happening, especially among children, even with the 120 F preset for water heaters.

One study, focused on New York City and published in 2007 in the Journal of Burn Care & Research, found tap water scald burns remained a significant public health risk, especially in older homes that were exempt from a city law that required water heaters installed in all apartments built or renovated after 1997 to be set to a maximum temperature of 120 F.

Around the same time, Shields and her colleagues began testing the water heater temperature of 976 Baltimore homes. They found about 41% of homes had their water heater temperature set above 120 F. In “Still too hot: Examination of water temperature and water heater characteristics 24 years after manufacturers adopt voluntary temperature setting,” published in the Journal of Burn Care & Research in 2013, the researchers found in more than half of the homes the water heater gauge setting was more than 10 degrees off at a higher temperature.

“What we found is there’s a relationship between the size of the water heater and the temperature of the water,” Shields says. “No one wants to run out of hot water for their shower, so if your water heater isn’t big enough, what a family will do is raise it up higher.”

Homeowners were more likely have a safe hot water temperature than renters (63% versus 54%), Shields and her colleagues found. Also, households whose income was above the federal poverty level were more likely to have a safe hot water temperature compared with those whose income was below the federal poverty level (62% versus 57%).

In their latest paper, Shields and her co-authors write thermostatic mixing valves are a promising solution to prevent scald burns at homes. They call for policy proposals that require the use of thermostatic mixing valves in all homes.

Current federal building codes for new plumbing require mixing valves at each faucet, but plumbing installed before the codes were adopted in 1987 are not included in the requirement. So, even though thermostatic mixing valves are recommended by water heater manufacturers and the International Code Council, their installation in older homes is not required in the U.S. unless the plumbing system is being replaced.

“My work for the last 10 or more years has been really just trying to raise the profile of this problem,” says Shields, “so that we understand that we don’t want to just systematically exclude people who live in older homes, which are more likely to be renters, more likely to be low-income families, from the protection of this really simple engineering solution that we have.”

Meanwhile, several countries have adopted the temperature mixing valves as a standard.

Since 2002, Australia has required that all new and replacement hot water systems must be fitted with a temperature control device to ensure the water temperature does not exceed 122 F.

Canada has mandated thermostatic mixing valves to be installed with all new water heaters since 2004.

And a few studies have assessed and reported on the effectiveness of the devices.

  • One study in Glasgow, Scotland, published in April 2011 in Injury Prevention, finds installation of thermostatic mixing valves as part of new buildings or major renovation with installation of a new bath in homes with children under the age of 5 is likely to produce cost savings.
  • Another study, published in Archives of Disease in Childhood in February 2011, also assessing the effectiveness of the mixing valve installation in homes with children under 5, find the devices “and accompanying educational leaflets are effective at reducing bath hot tap water temperatures in the short and longer term and are acceptable to families.”
  • One 1988 study published in the journal Burns notes the installation of thermostatic mixing valves at bath and shower outlets can “totally eliminate the risk of hot tap water scalds.” Even though installation of the valves in every household wouldn’t be feasible, “is a strong case for installing them in hospitals and residential homes for paediatric, geriatric and mentally/physically handicapped patients.”
  • And a study published in the Journal of Emergency Medicine in 1993 recommends installation of temperature-control valves in showers to prevent scald burns among people with disabilities, older adults and young children.

“I would like it to just be integrated in the water heater or required as an add-on to the installation of a water heater if it’s an older house,” says Shields.

Shields recently replaced the water heater in her house and asked the plumber to install a mixing valve. “And my plumber said, ‘You don’t need it. You don’t have young kids. You’re not old.’ And I was like, ‘Everyone needs it. I have had other people stay at my house occasionally and I just want to feel safe that even if I’m not there, that water is still safe coming out of the tap.’”

Related research

Burn injuries in the older population and understanding the common causes to influence accident prevention,” published in the journal Burns in June 2023, finds: “The main cause of burn injuries in the elderly of Yorkshire and Humber [England] was food preparation. The majority of the food preparation burn injuries were a scald burn due to the handling of hot fluids, either from a saucepan or a kettle. A prevention strategy aiming to make people aware of this finding can help reduce burn injuries in the over 65 years old age group.”

Pediatric major burns: a monocentric retrospective review of etiology and outcomes (2008–2020),” published in the European Journal of Plastic Surgery in April 2022, finds: “Scalds were the main mechanism of injury (70.1%) and upper extremity was the most frequent location affected (68%). The 28.6% of patients suffered some complication, but the mortality rate was low (0.7%).”

A state-wide analysis of pediatric scald burns by tap water, 2016–2018,” published in Burns in December 2020, finds “a significant number of scald burn injuries by tap water in children, particularly under 5 years.”

Burn Injury,” published in Nature Reviews, Disease Primers, in February 2020, finds, “Development of international burn registries should facilitate better understanding of burn injury aetiologies in many vulnerable populations.”

Pediatric Burns: A Single Institution Retrospective Review of Incidence, Etiology, and Outcomes in 2273 Burn Patients (1995–2013)” published in the Journal of Burn Care & Research in November 2016, finds “children 6 years or younger accounted for more than half of the burn-associated hospitalizations, and were more likely to be male children suffering scald burns.” Also, “Geographical analysis revealed significantly higher incidence of burns in areas with lower incomes.”

Preventing childhood scalds within the home: Overview of systematic reviews and a systematic review of primary studies,” published in Burns in August 2015, finds, “The paucity of evidence we found highlights the need for research to investigate the effect of interventions on reducing the incidence of childhood scalds in the home, the safe handling of food and drinks, and safe kitchen and cooking practices.”

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