On top of all the other tragedies that have hit the citizens of Flint, Michigan, thanks to the toxic water coming through their pipes, it appears that there have been 87 cases of Legionnaires’ disease, including 10 deaths. The disease is caused by bacteria, Legionella pneumophila. It's a temperature-sensitive bacterium, as noted in TreeHugger.

When water containing Legionella is atomized, like in a shower or a cooling tower, the bacteria can get into lungs and cause a pneumonia-like disease that is treatable with antibiotics but is pretty hard on the very young, the sick and the old — which is how those Legionnaires in Philadelphia were killed in 1976, giving the disease its name.

So what’s happening in Flint? According to mLive, the local newspaper group,

Officials said there’s no evidence of a clear link between the outbreak and the water system change that’s caused an uproar over elevated lead levels found in Flint children.

graph of casesLegionella epidemic curve in Michigan. (Photo: Michigan Department of Health via Forbes)

Well gee, you don’t have to be Sherlock Holmes to see a correlation between Legionella and the switch from Detroit’s pure Lake Huron water to the dirty river water in April 2014, where you see that instant spike. So what happened?

flint water supplyFlint's water is full of bacteria food. (Photo: Flint Water Update)

According to Flint Water Supply Updates, a project of the Virginia Tech Research Team, there's good reason to suspect that Legionella could be carried into homes. They write:

A key hypothesis of our National Science Foundation RAPID grant is that the rapid corrosion of iron water mains in Flint would dramatically increase growth of Legionella in buildings. Mechanistically, higher rates of iron corrosion will produce: 1) higher iron in water, and 2) lower levels of free chlorine. Both of these factors were confirmed to be present in Flint during our field sampling, and have been shown to dramatically increase Legionella regrowth in our recently published laboratory research utilizing simulated distribution systems.

I'm going to add a third factor into the equation: settings on American water heaters. I'm an architect and I live in Canada, where in 2000 there was a public health disaster in Walkerton, Ontario, a serious wake-up call about bacteria in water. Everyone in the business of buildings and cities learned a lot about water really quickly. After that, Canadians were advised to set their water heaters at 140 degrees minimum to kill bacteria. In fact, it’s the law. In new installations, water heaters must be set at 140 degrees and then a mixing valve is installed to bring it back down to 125 degrees to prevent scalding. I describe this in detail in a post on TreeHugger.

The reason is, as noted earlier, that the bacterium is temperature-sensitive. Here's what happens at different temperatures:

  • 70 to 80 degrees C (158 to 176 degrees F): Disinfection range
  • At 66 degrees C (151 degrees F): Legionellae die within 2 minutes
  • At 60 degrees C (140 degrees F): Legionellae die within 32 minutes
  • At 55 degreesC (131 degreesF): Legionellae die within 5 to 6 hours
  • Above 50 degrees C (122 degrees F): They can survive but do not multiply
  • 35 to 46 degrees C (95 to 115 degrees F): Ideal growth range
  • 20 to 50 degrees C (68 to 122 degrees F): Legionellae growth range
  • Below 20 degrees C (68 degrees F): Legionellae can survive but are dormant

Thats why most Canadian authorities, post-Walkerton, recommend that the water temperature be higher than 140; that's the temperature that kills the bacteria in a reasonable timeframe. The water in a hot water tank is stratified, and it is set at 120 degrees, it's probably cooler at the bottom, in that ideal growth range.

government photo re thermostatThe Department of Energy says, 'Turning down your water heater temperature can save energy and money,' but there are other things to consider. (Photo: DOA)

In the United States, the Department of Energy takes a different view. They recommend that people save energy and prevent scalding by turning down the temperature to 120 degrees. However they note:

While there is a very slight risk of promoting legionellae bacteria when hot water tanks are maintained at 120ºF, this level is still considered safe for the majority of the population. If you have a suppressed immune system or chronic respiratory disease, you may consider keeping your hot water tank at 140ºF.

So here we are in Flint, Michigan. You have municipal water with lots of Legionella in it, which would probably be dormant in the cold water line, and finds a perfect petri dish in the comfortably cool bottom of all those hot water heaters. And according to Dr. Judy Stone, who writes about medicine and ethics in Forbes:

Given that Legionella infections are caused by aerosolized contaminated water, as is seen with shower heads or decorative fountains, I am a bit surprised that the Michigan Department of Health and Human Services emphasized that there were no changes in recommendations for bathing or showering. In fact, they used this poster, now removed after an outcry, in an attempt to reassure the public:
shower poster

I feel I should reiterate that I was, until recently, an architect licensed by the Ontario Association of Architects, and had a responsibility to keep up to date on issues like this. I'm an adjunct professor teaching sustainable design at Ryerson University in Toronto. I have been railing about water heater temperature for years, complaining in a post six years ago that "there is a tendency in the States to assume that 'green' means primarily "saves energy," and that the DEA is far more concerned about reducing energy consumption than it is about the health of its citizens."

I'm pretty convinced that this is a contributing factor in this situation. Normally the water treatment system and the chlorine might keep the legionellae numbers down so they don't thrive. But here, you have lousy water that is full of the stuff, sitting with lots of lovely nutrients in a petri dish. What's the surprise?

Turn up the heat.

One way to reduce the amount of Legionella getting into the homes of Flint residents is to turn up the temperature on their water heaters. And it might be a good time for the Department of Energy to reconsider their advice on the subject.

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Has energy-saving advice contributed to Legionnaires' disease in Flint?
Are our water heaters acting as petri dishes for Legionella pneumophila?