Most water plants would be able to handle a chemical spill. Not all water plants even have carbon filters and most water plants are only secondary systems, not tertiary. Plus as you noted the chemical is not considered hazardous, so there is no reason the water plant would even be screening/filtering for it.
Activated carbon (AC) is generally used in water treatment for removing free chlorine and / or organic compounds. Removal of organics from potable water could be to prevent common organic acids such as humic or fulvic from reacting with chlorine to form trihalomethanes (a class of known carcinogens) or, to treat waste water to remove any number of organic compounds to make the water suitable for discharge. Similar to other types of water treatment, however, AC filtration is effective for some contaminants and not effective for others. AC filtration does not remove microbes, sodium, nitrates, fluoride, and hardness. Lead and other heavy metals are removed only by a very specific type of activated carbon water treatment and this would typically only be feasible for point-of-use household filters. Activated Carbon Filters
The issue in mind is how would a treatment plant know if a toxic substance had entered and wasn’t removed by treatment.