Health Canada released an updated guideline for trihalomethanes (THMs) in chlorinated drinking water today, May 19. THMs are chemical compounds that may occur when organic material in water is mixed with chlorine. The health risk of THMs remains extremely low although some studies link them to health concerns if there is very long term exposure. THMs are not an issue for Nova Scotians who use private wells as they are a byproduct of the chlorination process. Chlorine is used in many municipal water systems. Municipalities in Nova Scotia with THM levels that currently exceed the updated federal guideline are: Louisbourg, Liverpool, Tatamagouche, Mahone Bay, Baddeck, Hayden Lake, Shelburne, Sydney River and Antigonish. The updated federal guideline reaffirms the existing acceptable level of total THMs at 100 micrograms per litre. But, for the first time, it sets a new guideline for bromodichloromethane (BDCMs) — a component of THMs – at 16 micrograms per litre. The guideline also notes that THMs can be absorbed by inhalation and skin contact during showering and bathing, in addition to being ingested. Studies in the U.S. and Canada have suggested that high THM levels in drinking water may be linked to stillbirths or miscarriages. Those studies however have not proved a definite connection. Other studies indicate that high exposure to THMs over a lifetime may increase chances of developing bladder cancer. As a precaution, public health officials in Nova Scotia are recommending that Nova Scotians minimize their exposure in Nova Scotia communities where THM levels are higher than the new federal guideline. “While the science linking THMs with stillbirths and miscarriages is not conclusive, our advice is that pregnant women and indeed anyone in affected communities should restrict their time in the bath or shower to as short a duration as reasonably possible,” said Dr. Ann Roberts, medical officer of health for Nova Scotia. “People in the affected communities can also reduce THM levels in their drinking water by installing activated carbon filters certified to remove THMs or use bottled water from a certified supplier.” The Department of Environment and Labour has worked with the municipalities to reduce the number of communities with unacceptable THM levels from 23, to the nine listed above. That work is continuing. “As part of Nova Scotia’s Drinking Water Strategy, we are helping municipalities ensure their drinking water meets current public health standards, including meeting the THM guideline,” said David Briggins, manager of Environment and Labour’s water and wastewater branch. “Municipalities are eager to make sure their drinking water quality is superior and we appreciate their ongoing efforts.” THMs are formed when chlorine reacts with organic materials such as dead leaves that naturally occur in surface water. Chlorine is used to treat drinking water to kill bacteria that can cause serious illnesses. Information about THMs in drinking water can be found on the Environment and Labour website at www.gov.ns.ca/enla/water/thm.asp .