In addition to making solar panel roofs compulsory the government should pass legislation that forces people to use rainwater to flush their toilets – with one added extra.
All such tanks have a 10 or 20% reserve capacity for absorbing abnormal rainwater and alleviating floods. Normally when the tank gets to 80% excess water is let go; there is always a small reserve kept for times of emergencies. Then when there is a LOT of rain someone can flip a switch that remotely activates all of the emergency capacity in the rainwater collection systems of a given area and they start to fill their excess capacity.
So; suddenly in a given area all rainwater that falls onto a roof is held in a tank. I don’t know the figures but that has GOT to have an impact on flooding! – as well as helping out with water usage in general as suddenly no toilet is flushed with water from the mains but only with rain water.
The secret here is large tanks: dig up the garden and bury a huge mother of a tank; then use a small wind turbine to pump the water to where it is needed. Personally – as long as there was a small filter there – I would have no problem bathing in rainwater. It is a LOT more pure now than it waswith acid rain!
But as ever the free market would never do this because it requires captial expenditure to provide a small but long term benefit to the individual – as well as a long term benefit to society as a whole. So; make it compulsory and get a huge swathe of people employed in implementing it and make it possible to retrofit them with an interest free loan and a grant for 50% of the cost – and make it compulsory for all new roofs to have them in say 5 years time.