What can be done about bad CG water? Follow-up...

I am in the business of chemically maintaining irrigation lines preventing plugging from mineral and bacterial deposits. Just judging from your pictures and description of it being slimey I would hesitate a guess that it is some form of iron-fixing bacteria, which is not a health hazard but can play havoc on filtration systems. If it is a public health system they should be treating to prevent the formation of iron or hydrogen fixing bacteria.