The main water source for the city of Las Vegas is the Colorado River. This river is crucial for providing water to the city and surrounding areas, especially given the arid climate of the region. The lake formed by the river, Lake Mead, is one of the largest reservoirs in the United States and serves as a primary source of drinking water and irrigation. The management of the Colorado River is key to balancing water demand with environmental conservation, as Las Vegas continues to grow in a desert environment where water scarcity is increasingly prevalent.