For the past few weeks, crews from the East Bay Municipal Water District have been flushing the water system in an effort to eradicate a known cancer causing compound in two systems in Berkeley and in Orinda.
The contaminants are called trihalomethanes, or THMs, and they’re byproducts of the process used to treat water. The EPA limit is 80 parts per billion. Two of East Bay MUD's 16 sites exceeded the limit this year.
East Bay MUD representative Andrea Pook says the past years of drought combined with lower water use causes increased sediment in the drinking water supply. The contaminant THMs come from chlorine reacting with more plant debris in the water system than usual, due to heavy rains in the last few months.
“What happens is when you have chlorine, which is a disinfectant, which we need to protect from disease in our water; when that chlorine reacts with a naturally occurring organic material such as vegetation, and things like that, which would end up in a lake or reservoir, that reaction between the chlorine and the naturally occurring organic matter, creates byproducts, one of which is THMs,” says Pook.
She says East Bay MUD will continue flushing and monitor levels more frequently. In the meantime, she says, “The water is safe, East Bay MUD water meets all state and federal guidelines.”
David Sedlak, a professor of environmental engineering at UC Berkeley, says the preventative measures East Bay MUD is taking are not a cause for alarm, “because it’s more or less in the range of what we normally encounter this time of year with our water supply. I think if some of the concentrations kept going up as a result of some of the factors that East Bay MUD is concerned with, we might want to revisit it and start thinking about whether additional treatment is needed or an alternative disinfectant.”
So for most people, the water’s safe right now. But higher levels of THMs are known to increase the risk of certain cancers and reproductive harms. East Bay MUD advises pregnant women and immunocompromised individuals to consult their doctor.