Tradition holds that visitors can assure their return by tossing a coin over their shoulders into the water.
The estimated 3,000 euros ($4,000, £2,000) which splash daily into the Trevi are collected each night.
Charity Caritas says it plans to set up a supermarket offering essential items free of charge to Rome's needy.
Families will be given a top-up card by their local councils which they can swap for basic food items at the supermarket in central Rome.