Renewable energies (solar and wind energies) associated to reverse osmosis (RO) are gaining renewed interest for brackish and seawater desalination. Another potential source of energy is the hydrostatic pressure at a sufficient operative depth or height to perform the RO process. This article provides a comparison of the energy requirement of various hydrostatic pressure-RO plants. For submarine and underground plants, the required energy is equal to 2.98 and 3.54 kWh, respectively, for 1 m(3) of produced fresh water. In case of hydrostatic pressure generated by a column of water due to a head difference between the sea level and an adjacent mountain, the energy required is equal to 1.4 kWh. These energy requirements compare well with the usual energy requirement for desalination, between 3 and 10 kWh for 1 m(3) of produced fresh water. However, the main drawback associated with hydrostatic pressure plants relates to their construction and their maintenance, which are expected to be more complicated and costly than for a ground plant. (C) 2009 Elsevier Ltd. All rights reserved.