Or you do what Thatcher did in the UK. You require all factories that need water from rivers to have their water input below their waste water output. As all fa

Or you do what Thatcher did in the UK. You require all factories that need water from rivers to have their water input below their waste water output. As all factories need really clean water, this would force them to install top of the line waste water plants. That's how you deal with it efficiently.