Professor Colin Green's paper on the economics of retrofitting rainwater harvesting measures to households includes separating a surface water drainage charge with the general wastewater charge [ACA01].
A comprehensive study is needed on this and all other aspects of Blue Green strategies in order for valid comparisons to be made to grey alternatives as well as optimised solutions of blue, green and grey. Conflicting views need to be aired and debated with, preferably, transparent and independent evidence in support.
Sir Ian Byatt was Director General of the Office of Water Services (Ofwat) between 1989 and 2000, where he was responsible for independent economic regulation of the water companies in England and Wales. From 1978 to 1989 he served in HM Treasury as Deputy Chief Economic Adviser. Since 2000 he has advised the World Bank and governments around the world on matters relating to the water industry. Sir Ian, who was an adviser to the former Water Industry Commissioner from 2002, was knighted in 2000. His views on the financial and legal / regulatory risks associated with the Thames Tideway Tunnel are expressed in this paper [GAI18] and he provides a foreword to George Turner's paper on the value for consumers within which a better way forward for our utilities is discussed [GAI19, p43].
Comprehensive cost-benefit studies of blue, green and grey solutions have not been completed as part of an holistic value study for London and then disseminated to Londoners in order to help inform choice. In addition to the straight finances, the legal and regulatory risks associated with all approaches need to be understood and debated to further support an informed choice for the best way forward.