We first have to make a distinction. Of course, a Christian can use the Holy Water because he is a Christian, and if he believes in the power of prayer, God can give him actual graces. Sacraments such as the Holy Water, Holy Pictures, or the Holy Cross can transmit graces, especially if the person believes in them. For non-Christians, however, it could be difficult.
It depends on the person if he believes that the Holy Water is blessed by the power of Jesus Christ. He has to believe; otherwise, he might use it magically, and I think it is not good. If he does not believe that the Holy Water he receives is blessed by the power of Jesus Christ and His Cross, then it is better not to give it to him. He might think of it in a pagan way, as a magical tool.
Protestants can, of course, pray the Rosary because all prayers come from Holy Scripture. When they say “Sola Scriptura,” okay, the Our Father is in Holy Scripture, and the Hail Mary is said by St. Gabriel, and the Glory Be is the mystery of the Trinity, which is also in Scripture, and the mysteries of the Holy Rosary are from Scripture, thus the Rosary is biblical.
So, of course, Protestants can pray the Rosary, even though none of them do. Perhaps these prayers will bring them closer to the Catholic Church and the Catholic faith. Non-Christians, however, have to believe in what they say. When they utter the words “Our Father” and “Hail Mary,” they have to believe in these words, otherwise, the prayer will have no meaning. It may become a magical formula for them, and this should not happen. The Holy Rosary should not be used in a pagan way, as a magical formula. They have to believe in the Holy Rosary. Maybe they are catechumens who are preparing themselves for the Catholic faith.
Of course, even if they are not yet baptized, they can still use the Holy Water and the Holy Rosary, but they need to have the desire to come to the Catholic faith. It is a journey; like the catechumens in the old church, they were allowed to pray with Christians, not entirely but at least partly.
Dear visitors of Gloria Dei and all who have already written or who will write a personal message to me. I am grateful for your attention, your kindness, for your spiritual support and especially for your sacrifices and prayers for me. God may reward you!