The Hardwald (squeezed in between Muttenz and Birsfelden - between the Autobahn and the Rhine) has been used as an important drinking water reservoir since the 1960s. For this purpose, water from the Rhine is pumped up into the forest and guided through canals and into ponds. The water seeps away and is cleaned in a natural way. The infiltrated and cleaned water raises the groundwater level and can thus be used as a drinking water reserve.
In addition, it is a nice little hiking area!