Why are restrictive lids placed on some baptismal fonts?

If possible, churches should consider removing the lid of the baptismal font and placing a larger bowl on the stand. Baptismal bowls should be open and look receptive. They should not appear closed and exclusive. Baptism is God’s free gift to us. Baptismal bowl covers originated from a medieval tradition when people began stealing the “magic water” for their homes necessitating preventive lids.