Early in November, a number of Franklin County residents received what appeared to be a fairly frightening notice in the mail informing them that their drinking water contained trihalomethanes (THM), a group of chemicals with a long name unfamiliar to the average consumer of tap water.

In spite of reassurances in the letter that the situation is not an emergency, many people found the information worrying.

What’s the truth? Is the water safe to drink?

THM is a byproduct of the process by which our drinking water is purified. It is created when chlorine, a disinfectant, combines with naturally occurring chemicals in the ground water i.e. dissolved soil.

In 2002, the federal Environmental Protection Agency (EPA) and the Florida Department of Environmental Protection set new, tougher standards for the level of THM that is acceptable in drinking water.

Any time the amount of THM is higher than the legal limit, the agency providing the water to the public must report the excess to its customers, even if the amount of THM is only slightly higher than the acceptable limit.

Our county drinking water exceeds the legal limit by only a tiny amount.

For example, in Apalachicola, over the last year, on the average, the drinking water contained 82.33 parts per billion (ppb) of THM. That is less than three parts per billion higher than the legal limit of 80 ppb.

Not parts per million, parts per billion. It takes very sensitive equipment to detect the difference.

One THM with which many people are familiar is chloroform, which has been used for decades as an anesthetic.

At the high levels of concentration required to induce unconsciousness, chloroform can cause acute reactions in humans including irregular heartbeat, liver and kidney damage and redness and blistering of the skin. Exposure might possibly increase rates of certain cancers and cause a miscarriage or damage an unborn child as well.

The effects of THM are expected to be similar to chloroform, however, the level of exposure to inhaled chloroform that can cause injury is 1,500 ppb or more.  This is much higher than the 82 ppb found in our water.

Toxicologists tell us the poison is in the dose. Even pure water is dangerous if too much is consumed.

According to the EPA, 80 ppb is only 20 percent (one-fifth) of the amount of THM considered safe for consumption over a lifetime.

So is there a risk in consuming tap water here?

Perhaps a very slight one, if the water is consumed over many years, but THM in our tap water is probably not something to lose sleep over.