Particularly within Europe, ever increasing amounts of industrial and commercial roof space are being drained using siphonic roof drainage. One installer claims it system drains over 60 million square meters (646 million square feet) of roof area. This increase in usage is largely due to the many advantages the systems have over "conventional" systems for equivalent sized roof areas.

However, notwithstanding the increasing use of these systems, there are still uncertainties regarding just how these systems operate--particularly during priming. This lack of understanding of system operation means that if a system fails, it is often difficult to appreciate why the failure has occurred. Furthermore, as siphonic systems design necessitates a higher level of expertise than is required for convention systems, the performance of these systems can be more reactive to small inaccuracies and erroneous assumptions. To resolve this, over the past five years there has been an increasing amount of independent research underway attempting to understand how siphonic systems actually perform. This article aims to collate this work, and give an overview of how siphonic rainwater systems operate.