The type of water heater you choose plays a significant role in the overall cost. Once you have securely connected the water supply lines to the water heater, it’s time to turn on the water supply. Slowly open the main water supply valve to allow water to flow into the water heater. Once you have successfully installed your water heater, the next step is to connect the water supply. This is an important step in ensuring that your water heater functions properly and provides you with hot water whenever you need it.