Abstract: A reservoir system consisting of a nonwoven made from thermoplastic polymer filaments, shaped into a closed bag containing a water-soluble active principle. The bag is intended to ensure a prolonged release, progressing linearly, of the active principle in an aqueous environment. For a given active principle, the desired diffusion kinetics are obtained by adjusting, depending on the availability of the active principle, the surface area of the nonwoven and the degree of hydrophily of the latter. To this end, it is impregnated, either with polysiloxane or a quaternary ammonium salt, or with a perfluorinated compound or an acrylic resin and paraffin.