It depends on the water heater. If it is a gas water heater, you will definitely need a plumber, as they must be installed by a licensed professional. If it is an electric water heater, you may or may not need a plumber, depending on the model. Some electric water heaters are designed for easy installation by homeowners, while others require professional installation. So it really depends on the specific water heater you are looking to buy. Consult the manufacturer's instructions to be sure.

It depends on the type of water heater. If it is a gas water heater, then you will need a plumber to install it because they have to hook up the gas line. If it is an electric water heater, then you can probably install it yourself, but you might need a plumber to help you with the wiring.