Please see below a profile and plan view of a drawing of a standard rainwater harvesting cistern located on a private/public property's frontage with either a high water table or contaminated subsoils, connected to the building's downspout. This example includes the use of a raingarden as a pretreatment option, along with an underdrain and overflow which both deposit treated rainwater into the holding cistern. If water is not used for irrigation purposes, etc. there is an attached overflow which connects to the municipality's storm sewer system.
Drawings are from the [https://www.toronto.ca/ext/digital_comm/pdfs/transportation-services/green-streets-technical-guidelines-appendices-v2-17-11-08.pdf City of Toronto's Green Streets Technical Guidelines Appendices] document. For further details about these cross section drawings please visit the link.