Rainwater tanks often provide a reliable and affordable water supply source in rural and remote areas where piped water supply systems are unfeasible due to economic considerations. However, over recent decades there has been an increase in the adoption of rainwater harvesting as part of the water supply source mix in modern cities. The uptake of rainwater harvesting has been influenced by the rise of ecological sustainable development as a mainstream practice. Rainwater harvesting is now implemented as part of an integrated urban water management approach to alleviate pressure on traditional water supply sources due to increased demand, driven by the rapid growth of urbanised populations. While examples of rainwater harvesting in human settlements can be found since ancient times, there are still gaps in understanding the role that it can play in modern cities. This paper reviews current international experiences with rainwater harvesting, particularly examining the drivers for their adoption in different urban contexts and the impediments faced for greater mainstream adoption. The paper then reviews the current state of research associated with understanding the value of rainwater harvesting in modern cities, which include impacts on reducing mains water demand, public health risks, energy implications, environmental impacts, and cost-effectiveness.