Over the last 30 years, a large amount of research about air PVT collectors has been carried out, but the most investigated PVT technology in recent time is based on systems using water as the heat transfer fluid, because they achieve higher overall efficiencies than air systems, due to the higher heat capacity of water. In this sense, this article presents an extensive review about water flat plate PV-thermal collectors, which are the most widespread in the current market. The review is subdivided according to the elements that compose PVT collectors, from the cover to the insulation material, identifying the most important design parameters of them. This article gives an up-to-date review of the technology, with a specific focus on technological progress in recent years and on the future development. (C) 2014 Elsevier Ltd. All rights reserved.