Abstract: Composition for use in a water tank in the kitchen or sanitary sectors characterized by a basic composition essentially evolving its function following addition to a first water filling of the water tank, in the form of a tablet and at least one particle, with at least one core, which comprises at least one substance evolving its function essentially following an at least partial emptying of the first water filling from the water tank Ad and the inflow of fresh water and a covering substantially completely surrounding the core or cores comprising at least one compound, whose solubility increases with decreasing concentration of a specific ion in the surrounding medium, the at least one particle being so arranged in or on the tablet that the surface of the particle or particles is at most only partly in direct contact with the surface of the basic composition surrounding the same and the concentration of the specific ion in the local environment of the particle or particles is sufficiently high up to a substan