Peel the peaches, remove the pits, and cut into quarters. Rinse the peels and add them to 3 cups water (about 700 ml). Bring to a boil for a few minutes, then remove and discard the peels. This will infuse the water with a peach aroma.

After removing the peels, add the peach quarters to the boiling water and cook for about 5 minutes. Remove the peaches and immediately place them in a bowl of ice water.

Continue simmering the peach cooking water. Add the rock sugar and stir until dissolved, then add sliced ginger. Cook until the syrup thickens slightly, then turn off the heat and let it cool. Once the peaches in the ice water are cool, drain them well.

When the syrup has cooled, pour it into a clean jar and add the peaches. Let the jar sit in a cool place for about 2 days so the peaches absorb the syrup. To serve, brew a packet of peach tea with hot water, then add some preserved peaches and syrup, plus a thin slice of calamansi or lemon for a sweet-tart, refreshing drink.