Accounting of energy-related GHG emissions in the water sector have largely been conducted at single utilities or cities and rarely at a regional or country scale. In this study, we assess the carbon footprints of operational energy use for 76 wastewater utilities and 64 water utilities across the United States. Additionally, we investigate water-related GHG emissions at a sub-annual scale through three case cities to understand how GHG emissions change at the monthly scale. We estimate the total drinking water and wastewater GHG emissions associated with electricity, biogas, natural gas, and fuel oil consumption across the United States to be 26.5 x 109 and 20.1 x 109 kg CO2e respectively. We find the average GHG emissions per unit drinking water and wastewater emissions to be 0.463 kg CO2e/ m3 and 0.42 kg CO2e/ m3, respectively. The research provides insights into operational GHG emissions of the water sector and advances the understanding of temporal variations in the life-cycle of energy use