Rainwater harvesting systems can play an important role in helping to prevent down-stream flooding, by storing some of the rainfall at source, rather than releasing it immediately into the drainage infrastructure.

Avoiding the rainfall that falls on roofs and roads adding to down-stream flood risks (know as SuDS, or sustainable drainage), will usually be a Planning Condition on all new developments; meeting this condition will vary from place to place, depending on local conditions.

An optimum approach to meeting these and other water-related regulations applying to new developments, is for Architects to take into account both surface-water management and water-consumption considerations at the project design stage; an integrated rainwater harvesting and SuDS system, along the lines illustrated below, provides a cost-effective way of helping to meet all the requirements of the 2010 Flood & Water Management Act.