Lets just think of the ways.
1: No electricity to run the pumps
2: No chemical deliveries for the treatment process
3: No parts for maintenance and repairs
4: Not enough money (or money that is worth anything) to
hire and retain the Water Quality Control lab people
5: Not enough money (see above) to keep a maintenance and
repair staff in the Facility
6: No Electricity, no Chemicals, no Parts, no Personnel,
no money to train new personnel.
In short the vendors who would normally supply the plant personnel with the tools and materials to do their jobs are not going to give their stuff away for free, the mechanics and chemists who actually operate the plant are not going to give their knowledge and labor away for free.
If you were one of those mechanics or chemists, would you take what you know to be worthless currency in exchange for your labors, or would you take your knowledge and experience into the Black Market in order to KEEP your FAMILY FED?
I worked full time in Water Treatment and Distribution for many years (grade 3 Treatment, grade 4 distribution), there are thousands of ways to shut down a plant, primarily logistics and maintenance.
Same holds true for Waste Water Plants.
Let them drink salt water.