The answers at How long does water need to be boiled for to kill all bacteria / viruses? indicates that boiling water kills bacteria & viruses. But boiling does not remove any chemical contaminates that might be present. Neurotoxins are not "alive" so they can't be killed, though some like botulinum toxin are denatured by heat.
Historically the practice of boiling vinegared wine in lead pans to sweeten it was problematic. This was not due to a change, but rather leaching from the container (lead pan) to the fluid.
Are their any contaminates that might be present in water, that would become more toxic when boiled in modern containers?