(6)In relation to lead, the WHO recommended retaining the current parametric value, but noted that concentrations should be as low as reasonably practicable. Therefore, it should be possible to retain the current value of 10 μg/l for 15 years after the date of entry into force of this Directive. By the end of this transitional period, at the latest, the parametric value for lead should be 5 μg/l. In addition, since existing lead pipes in houses and buildings are a persisting issue and since Member States do not always have the necessary authority to impose the replacement of those pipes, the value of 5 μg/l should remain aspirational when it comes to obligations related to domestic distribution systems. However, for all new materials that come into contact with water intended for human consumption, regardless of whether they are to be used in supply or domestic distribution systems, to be authorised in accordance with this Directive, the value of 5 μg/l should apply at the tap.