Bring water and rice to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until rice is tender and water has been absorbed, 20 to 25 minutes. Remove from the heat and cool to room temperature, about 30 minutes. Refrigerator 8 hours to overnight.
Melt butter in a large frying pan or wok over low heat. Add onion and garlic; cook until onion is soft, about 5 minutes. Add bacon and frozen vegetables; fry until bacon is cooked through, 7 to 10 minutes.
Add cold rice and stir until rice is completely coated in butter. Season with salt and pepper and cook until heated through, about 5 minutes.