Rainwater runoff is increased by as much as 55% on the city end of a simple rainwater runoff-retention scale, from around 10% runoff in an undeveloped ‘naturally covered’ landscape. Simultaneously soil infiltration is reduced from up to 50% in natural cover landscapes to as little as 15% in our largely impervious city-surfaced environments. It is within this scale of runoff that opportunities exist for the in and ex-situ harvesting of from small to significant amounts of rainwater that would at once reduce stormwater runoff, increase rainwater retention and supplement centralized city water supplies. Rainwater harvesting, practised with other regenerative approaches to urban planning, is crucial to reducing stresses on hydrological processes and the life-supporting ecosystems services upon which our long term water security relies.