How do Roman Catholic sacraments differ from sacramentals such as holy water and blessings?

In Roman Catholic theology, a fundamental distinction exists between the seven sacraments and sacramentals, such as holy water or blessings.12

The Sacraments

The seven sacraments—baptism, confirmation, the Eucharist, reconciliation, anointing of the sick, marriage, and holy orders—are believed to have been instituted by Jesus Christ. They are considered "visible forms of an invisible grace" that function ex opere operato ("from the work done"). This means their effectiveness is derived from the saving act of God in Christ rather than the personal virtue of the minister or the recipient.324

Sacramentals

Sacramentals, by contrast, are sacred signs or objects—such as holy water, medals, candles, or verbal blessings—that do not share this same divine institution. They are symbols of personal prayer and dedication. Unlike sacraments, sacramentals are not thought to convey divine grace ex opere operato; instead, their effectiveness is measured by the faith and particular dispositions of the person using them.32