Unless something occurs making the Host not fit for consumption, the person ministering Holy Communion usually consumes the Host himself or herself in a discreet manner after everyone else has received. A Host dropped onto a reasonably clean floor or carpet in a church should not necessarily be considered unfit for consumption, but a Host that has been in a communicant’s mouth who has been unable to swallow would be (this sometimes happens when the Blessed Sacrament is taken to patients in hospitals or nursing homes.), as might a Host dropped onto a floor where serious health issues might exist, such as a hospital. In such cases, the person ministering Holy Communion generally has to use his or her best judgement.
If a Host is rendered unfit for consumption, the Host should be brought back to the church (if the Host was outside the Church) and dissolved in water until the appearance of bread no longer exists. The water with the dissolved Host should be poured down the sacrarium and the vessel in which it was dissolved carefully rinsed and poured down the sacrarium as well.