Method for disinfecting a filtration works (F) for the pretreatment of salt water, particularly seawater, upstream of a water desalination unit (1) using a reverse osmosis membrane, whereby an operation of disinfecting the filtration works is carried out periodically by adding a bactericidal agent to the water that is to be pretreated, the filtration works being periodically subjected to a declogging operation the operation of disinfecting the filtration works (F) is carried out during a declogging operation, and the liquid used for the declogging is formed of an aqueous declogging solution the salt content of which differs from the content of the water being pretreated the bactericidal agent is added (14) to the declogging solution upstream of its injection into the filtration works (F). (Figure 1)
