According to the Question Box moderator, Lourdes water is used to make Sacrosticky and can be used to repair broken statues of saints or rosary beads [Saint Fidgeta and Other Parodies; 40].
Our Lady of Lourdes is the name used to refer to the Marian apparition said to have appeared before various individuals on separate occasions around Lourdes, France. In 1858, the Virgin Mary allegedly appeared to a peasant girl named Bernadette Soubirous. Since that time, the site has been visited by millions of Catholics each year, with Lourdes becoming one of the greatest pilgrimage sites of the world. Bellairs was somewhat familiar with how the French grotto appeared because the University of Notre Dame has had a scale model on its campus since 1896.
Lourdes water is water that flows from a spring in the grotto at the shrine; bottles were carried home in the hope that a miracle might be transferred to some unfortunate who could not make the pilgrimage. Large numbers of sick pilgrims travel to Lourdes each year in the hope of physical healing or spiritual renewal.
Sacrosticky is a play on the word sacristy, the name for a room next to the altar where the priest's vestments were kept, and from which he would emerge to begin the Mass.