It provides a basis for the drilling and dimensioning of horizontal boreholes and the construction of horizontal filter wells. This Code of Practice does not discuss cut-and-cover methods - protected by e.g. pit lining - that are sometimes used in the field. Aimed primarily at contract awarding parties and planners, this Code of Practice intends to offer help in evaluating horizontal catchment systems from both a technical and economic point of view, determining the type of construction that best corresponds to the geological conditions of the site and finding the optimal design for a horizontal filter well. Answering the question of whether a horizontal filter well or a series of vertical filter wells would provide the best solution requires taking into account, among other factors, the site-specific hydrogeology as well as investment costs and overhead.