Scrutiny trip to Wargrave sewage works on the Loddon this morning, thanks to Thames Water, it was very interesting. We asked about sewage overflow into rivers and Thames Water explained it's largely down to heavy rain which overwhelms works with too much ground water which dilutes the sewage, they have huge overflow tanks but if that isn't enough the dilute sewage may overflow into the river. Main work they do is preventative - making sure builders haven't connected rainwater drainage into the foul system, looking for pipes that are letting water in - because they have been damaged etc
I also asked about the issue I had been alerted to in Sonning where residents complained of sewage in a small stream behind their houses. I will follow up with Thames Water today. I also asked about local builders who had caused problems with connections to new housing estates and how Thames Water maintained ditches, both hot topics around here.
This particular sewage works includes an anaerobic digestor rather than the filter beds we are more used to and generates power which is a good use of energy from the process of dealing with effluent.
Their two pleas were don't put anything down the toilet apart from human waste and toilet paper and please don't connect gutters to the mains drains. They were also keen to get a waste water directive implemented so builders could not connect clean water drains to the foul system by regulation.