Methods for introducing a substantially uniform concentration of a functional agent into a flowing stream of water using a shaped composition. The composition may be shaped and sized to be inserted into a device configured to be attached over the end of a faucet. The shaped composition comprises a dissolvable region including a functional agent (e.g., an anti-microbial sanitizing agent). A non-dissolvable region disposed adjacent to the dissolvable region may optionally be provided. The substantially non-dissolvable region remains substantially intact as the dissolving region is progressively dissolved, introducing the functional agent into a flowing stream of water.