'Mäertesbuer' means Saint Martin's well.
'Mäertes' is Saint Martin: the Fond Saint-Martin is called Mäertesgrond in Luxembourgish. A 'Buer' is a well that supplies water. Saint Martin is also the patron saint of Weimerskirch church. We have not yet found out where the well was, or whether it took its name from the church.