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07/07/2005: "Pesky Old THN Still In Some County Waters"

(Trout Lake - Water Source For Friday Harbor Water System-TFH Photo)
The town of Friday Harbor wants it's drinking water customers to know the water in Trout Lake still has, from time-to-time, slightly elevated levels of Trihalomethanes (THM), which are byproducts that are created when organic material in the lake is subjected to chlorination. Trout Lake is not the only lake in the county that has this problem, other water systems that draw water from surface lakes can, and have had, levels of THM that exceed the higher standards that have been imposed by the State. PAST STORY

While THM has been identified as a possible carcinogenic, it is important to known the levels adopted by the State are set at a level designed to protect those most at risk, and at a level most likely to protect the health of the consumer; and also to legally protect the water provider. If the State recommended levels are set high enough that expert witnesses could state the levels are higher than required to protect the public health, then the water provider is less likely to be held accountable in a legal action. On the down side of raising the levels, is the expense that results for those towns and communities that pull water from lakes, for it is difficult and expensive to lower the THM levels.


The Town report states: "The County's water supplies are tested on a regular bases as required by the State. The tests has shown that some of our water supplies from surface waters has exceeded the recommend levels of (THM) by a small percentage. The state standards are round numbers (80 ug/L = micrograms per liter -same as parts per billion), and the levels of some of our local water supplies have exceeded those numbers at certain times over the year. The Town of Friday Harbor has, for example, had an average level of 82.70 ug/L, with a high of 112.7 and a low of 54.3.

It has been suggested that homeowners can install filters to remove the THMs, but before you install an activated carbon filter, you may want to consider the potential effectiveness of removal of contaminates. Research has indicated that activated carbon is an ideal medium for growing bacteria. If there is no bacteria in the source water, there is little reason for concern, but if the source water does contain bacteria, then the filter can become a home for new bacteria growth that will in time close off the openings in the filter, causing it to be less efficient in filtering. It is still unclear whether the bacteria growing on the carbon poses a health threat, or whether they are harmless.

There is also the problem of the effective life of any filter -even if blockage by bacterial is not a problem. Bear in mind that the gallons of water used per day by two people is, at the high end, 120 gallons a day. Faucet-attached and countertop styles have a filter life of only 100 to 3,000 gals. An under counter type has only 3 to 4 thousand gallons, and the in-line types only 100 to 200 gallons

And last but not least, even the most effective filters will not remove all of the THM. The percent of removal range is from 33 to 62 percent, and as noted above, these numbers quickly drop with the use of the filter, and a lack of replacement and maintenance of the filter will quickly negate even the minimum treatment that a new filter can provide.

In short, the use of individual home filters is considered by health officials to be a temporary solution, both in terms of the effectiveness of the filters, and the long range health goals of government.

If one is concerned enough to take some action, it seems the best solution is to limit the intake of water from the effected water systems and use an alternate source of water for drinking. But bear in mind that the exceeded levels of THM in our drinking water are not high, and for some of the systems have been at low levels 50 percent of the time.