Discharging a water treatment plant into an open water course (ditch / brook)

[ProDave]

I had to get permission for ours as in Scotland SEPA discourage waste discharging to a watercourse and you have to get permission.  But I think the riparian rights you are talking of just mean you must not pollute the water and must not extract or add more than permitted amounts. Since the output from a recognised treatment plant is allowed to discharge into a watercourse, then by definition discharging that is not "polluting"  the watercourse.

[Dave and Helen]

Thanks for the additional details, all really helpful.

Dave C