Is it valid to baptize multiple persons at once? To take an extreme example, if a person is on a plane that's about to crash, and she wishes to perform a baptism that is valid according to the Catholic Church (and therefore valid according to the many other churches that have the same practices of baptism), should she open the nearest water bottle and:


Say "I baptize you all in the name of the Father, and of the Son, and of the Holy Spirit" while splashing the water towards the heads of the intended recipients of baptism, thus baptizing at least those who had not already been baptized? Or should she:
Say "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit" while pouring the water onto the head of the nearest person, and then proceed to the next person, and so on until death,


because the first option would not be a valid baptism? (Assume that this person is a child that cannot hope to land the plane, that she believes in the same God as Catholics, that she intends to bring the recipients of baptism into the fullness of Christ's Church, that air pressure is lost leaving no more-competent passenger conscious, and that the would-be recipients are a large number of lapsed family members, some of which have been putting baptism off for so long that there is reason to believe that their desire for baptism is at least questionable...)

Put a bit more plainly:

If a Catholic wishes to administer a valid baptism to many people in danger of death, must she baptize each person separately, or can she baptize all of them in one act, and what would be the correct form for doing so?
The rite of the baptism in the Catholic Church used to be in three forms: immersion, affusion or aspersion.

However the rite of aspersion as well the rite of affusion have been set aside in the western Catholic church due to practical and liturgical reasons. 

Is it still possible to baptize multiple people by aspersion.

According to this source: "Although, as we have said, immersion was the form of baptism that generally prevailed in the early ages, it must not thereby be inferred that the other forms of infusion and aspersion were not also employed and held to be valid. In the case of the sick or dying, immersion was impossible and the sacrament was then conferred by one of the other forms. This was so well recognized that infusion or aspersion received the name of the baptism of the sick (baptismus clinicorum). St. Cyprian (Epistle 75) declares this form to be valid. From the canons of various early councils we know that candidates for Holy orders who had been baptized by this method seem to have been regarded as irregular, but this was on account of the culpable negligence supposed to be manifested in delaying baptism until sick or dying. That such persons, however, were not to be rebaptized is an evidence that the Church held their baptism to be valid. It is also pointed out that the circumstances under which St. Paul (Acts 16) baptized his jailer and all his household seem to preclude the use of immersion. Moreover, the acts of the early martyrs frequently refer to baptizing in prisons where infusion or aspersion was certainly employed."