Tan Tan, a city of 50000 inhabitants, is located in the arid, water scarce south of Morocco. It is presently supplied with fresh water from a ground water aquifer through one of the longest mains (130 km) in Morocco. The reserved amount (about 4000 m(3)/d) for Tan Tan City hardly satisfies present fresh water needs. The future needs of potable water, crucial for Tan Tan City's social and economic development, will be supplied by non conventional resources using brackish water or seawater as an unlimited resource. A tender has been issued for a 3500m(3)/d brackish water treatment plant of to cover Tan Tan's water needs until 2007. To select the most appropriate and economical solution, especially in terms of energy, for a long-term water supply for Tan Tan City and to master new technologies, ONEP conducted technical-economic studies on the following thermal and membrane technologies and on fossil, solar, gravity and nuclear energy sources taking into consideration long-term environmental impact: seawater reverse osmosis desalination using an electric distribution network; thermal desalination (MDF) using energy extracted from a solar pond; reverse osmosis desalination (RO) using gravity energy via mining technology; thermal desalination (MED) coupled with a nuclear reactor of 10 MW. Wind energy is also being considered.