The main kind of water heater you are likely to have installed by an electrician is an immersion heater, which is an element that is fitted inside an existing or new water tank. There are water heater systems, a little like a gas combi boiler, that heat water over an element, but these are rarely used domestically nowadays.
The immersion itself is a standard piece of kit and the cost of the installation will largely depend on how much work there is to do. If this is a replacement water heater then all the other kit and connections should be in place. If this is a new heater, then a tank may also have to be installed and hooked up to the water supply, thermostat and timer.
Your electrician will have to drain an existing water tank to install an element for heating. He may place this in a protective sheath to make it last longer, as your water tank can cause the element to collect calcium build-ups in much the same way as the element in your kettle. You should always hire an electrician who is used to working with plumbing as well for this kind of job.
Ready to get started?