The Toledo water supply shut down. Why “boil water” advisories were not enough

Unlike other public water supply interruptions, municipalities affected by the Harmful Algal Bloom in western Lake Erie were dealing with something more than bacterial contamination.

Recent events in Toledo and parts of southeast Michigan may have water customers wondering why the usual “boil water” advisory was not issued. If the problem was blue-green algae (technically cyanobacteria) which are living organisms, then wouldn’t boiling your tap water kill them? The answer is “yes” but killing the organisms would not make the water safe.

Many water supply customers across Michigan have experienced “boil water” advisories in the past. These are usually in response to a water main break or repair. Any type of breach in an underground water main pipe creates a potential pathway for pathogens (usually indicated by the presence of E. coli) to enter the water supply form surrounding soils. These living organisms are usually susceptible to high heat and can be killed by boiling the tap water.

A Harmful Algal Bloom (HAB) in the water supply itself, Lake Erie, caused the recent problem in Toledo and southeast Michigan. Toxins, known as Microcystins are chemicals not susceptible to boiling. They are released by high concentrations of the living algae, Microcystis. These blue-green algae are the most common HAB in Lake Erie and it releases Microsystin – a known liver toxin harmful to humans and animals. So yes, boiling the water would kill the Microcystis algae but would not destroy the Microsystin toxin released by the algae. Unfortunately, in this instance the concentration of Microcystin in western Lake Erie was dangerously high – requiring a shutdown of water supplies. As such, municipalities were scrambling to provide alternative water sources instead of simply issuing “boil water” advisories.

So where does your drinking water come from? Could it be contaminated by a HAB? Since blue-green algae are aquatic organisms that occur mainly in surface waters, only those public water supplies that depend on surface water could potentially experience a problem with HAB’s. The Michigan Department of Environmental Quality maintains a list of public drinking water supply systems that includes the water source for each of those systems.

In addition, a recent Michigan State University Extension article provides readers with information about what to do in the event of HAB contamination of their pubic drinking water supply.

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