The build

Is it bureaucracy gone mad?  All the rain water from your roof has to go through a treatment plant,  all the rainwater falling in and around the roof of the house for miles around goes into the ground and thereafter into the watertable.  Same rain same end point. Or am I missing something? It's not for foul water is it?

Treatment plant is for foul water. But the rain water from the roof still has to go through many different pointless hoops. Including pipes, gravel pit and a restriction thingy. 
update coming soon.

By foul water do you mean sewage or just grey water? I'm (by that I mean P)  is fascinated by it all, thanks for sharing.  That treatment thingy must be a complex bit of kit. Having encased it in concrete, I hope no one wants to get at it again in the future. I'm off to Google treatment plants to learn more.  Every day's a school day.

https://www.drainagesuperstore.co.uk/bro...tries.html . We have the top one in this list