All new buildings and roof alterations to have a condition of adding in a water capturing tank of no less than 2,000 litres, appied through the Councils. NZ with its geological make up, is constantly at (low) threat of disruption through volcanic or seismic upheaval. At these times, it will be very useful to have thousands of water reservoirs in the areas locally affected. At the same time, during deluges, it will be very helpful to have millions of litres being collected in these tanks as a buffer against over delivery of massive amounts of water which may/will overload the systems from time to time.
In Auckland, there have been cycles where water supply has been rationed and this will be a balance for this also