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Proper Water-Heater Temperature

In your June issue, plumbing contractor Dave Yates makes a comment I find very hard to believe (Q&A, 6/06). He states, "Estimates of the number of deaths from potable hot-water system bacterial infections range widely, but 10,000 per year is the middle ground."

The article does not state whether 10,000 per year is an estimate for the United States or for the entire world, but either way, this number seems unbelievably high to me. Please elaborate if you have any more information on the subject.

Gary Dresser Dresser Homes Atlanta

Dave Yates responds: Actually, I suspect that the number is low, but others who look at the same data might arrive at a different conclusion. My estimate is based mostly on statistics concerning legionellosis, or Legionnaires' disease (LD), a pneumonialike illness caused when water droplets containing legionella bacteria are inhaled or aspirated.

In the United States, fewer than 2,000 official cases of LD are reported each year, but the national Centers for Disease Control and Prevention estimates that between 8,000 and 18,000 Americans are infected with the disease annually. Many more cases, CDC scientists say, are not reported or are misdiagnosed. For example, some researchers believe that anywhere from 2 percent to 15 percent of the 600,000 patients who enter hospitals each year with community-acquired pneumonia actually have LD.

Estimates of LD's mortality rates range from 5 percent to 30 percent. The elderly and people with weakened immune systems are most vulnerable. So if there are 80,000 or 90,000 cases of LD per year — and I've included patients misdiagnosed with community-acquired pneumonia in that number — there could be as many as 16,000 to 18,000 Americans dying of the disease every year, based on a 20 percent mortality rate.

How many of those cases are caused specifically by hot-water-system bacteria? That's hard to say with certainty. Legionella bacteria are quite common (in low culture numbers) within both municipal and private potable water systems. Most outbreaks have been traced to water systems, which can deliver bacteria to such amplifiers as cooling towers, humidifiers, and even supermarket vegetable misters. And research has shown that a hot-water system set at 120°F (rather than 140°F) can provide the perfect environment for legionella bacteria.

My own investigation into this problem leads me to believe that potable water systems — and hot-water tanks and their associated plumbing in particular — are the primary cause of these infections. Whether we're talking about hospitals, nursing homes, hotels, or residences, it just makes sense to reduce the risk by turning up the heat in hot-water storage tanks to 140°F — and then to protect end users with mixing valves and antiscald faucets.

Should Have Known

As a new subscriber, I noticed in my first issue a review of the new Bosch impact driver (Toolbox, 5/06). The author begins, "I like to think that I keep up with building trends and new tools, so I was surprised to find a whole new category of power tools that I was completely unaware of: cordless impact drivers."

Exactly where has this gentleman been plying his trade that these little gems have somehow escaped his notice for at least the last three years? Outer Mongolia? This is not the sort of thing that instills confidence in the readership of your publications.

Mitch Moschetti Fletcher, N.C.

Performance Guidelines Defended

I want to set the record straight about the purpose of the NAHB Residential Construction Performance Guidelines (In the News, 5/06).

The publication enjoys great success in the marketplace, which indicates that both homeowners and the industry find it very useful. It was created by a panel of more than 300 builders and remodelers with input from trade associations and insured warranty providers, among others.

The guidelines are a tool for evaluating residential-construction contract performance when there are questions about what constitutes acceptable practice. Contractors often refer to these guidelines in their contracts to establish mutually agreed-upon criteria for resolving warranty issues and to allow for less contentious dispute resolution.

The guidelines are an excellent resource, but they do not supersede building codes and local regulations, nor do they replace manufacturers' installation instructions.

Jerry Howard, CEO NAHB Washington, D.C.

Preventive Maintenance: No More Sewer Backups

A couple of years ago, a group of like-minded remodeling companies began to meet monthly to share our trials and tribulations and to learn from each other.

Recent discussions turned to plumbing blockage on a large project where the clients had moved out for a couple of months. The group experience was that there was often a problem with sewer backups after clients moved back into a house.

Our conjecture is that old debris in the pipes stayed soft with constant use, but once the family moved out the gunk had the opportunity to harden. It then caused problems when the family resumed residence.

Several of us now routinely snake the drains before clients move back in.

Mark Scott Mark IV Bethesda, Md.