The invention relates to a method of producing membranes for nanofiltration, ultrafiltration or microfiltration modules which are intended, for example, for water treatment, said membranes comprising a hydrophobic polymer material having a hydrophilic polymer material incorporated therein or deposited thereon. The invention is characterised in that it comprises the following steps consisting in: (a) cold conditioning the membrane, following the incorporation or deposition of the hydrophilic polymer material, in a solution containing ammonium, sodium or potassium persulphate; and (b) hot crosslinking the hydrophobic and hydrophilic polymer materials forming the membrane, at a temperature greater than 60 DEG C, by soaking said membrane in a crosslinking agent employing a radical mechanism.