Why would a municipal water system be “hackable”? IOW, why is there a connection to the internet? Serious question. Why would the water system have outside computer access? I can’t think of any reason.
These are not your grandpas waterworks. Everything is computer monitored, controlled and continuously optimized/updated for peak savings.
Some of the best waterworks equipment/filtration is made in Europe/Israel and sometimes requires remote tech support from a handful of experts that cannot physically fly everywhere. They can change the control code and get real time feedback from the plant to optimize it anywhere on earth.
Remote control is also very convenient for operation/maintenance for many many reasons at a big plant. One man with a tablet can do the troubleshooting/maintenance alone that used to take several men with radios in the old days.
It is all potentially inconvenient for this one reason though- hacking. Security will need to continuously improve but I doubt internet control is ever going away