I don’t think folks here appreciate the shear volume of water we are discussing.
Plus the fact that such a huge percentage leaks out along the way...
You would have to dump oil drums of poison in multiple places to make any difference.
Now, if you wanted to make a mess, you could affect the water delivery with a few sticks of TNT...but that is a different issue.
It’s not the real threat that is effective but the fear of a threat that will get people riled. People don’t know the difference between ppb and ppt for sure.
During the Fukashima disaster, there were reports of radiation in rainwater that was less than that found in a banana, but that did not stop talking heads on TV from freaking out.