The answer is yes, no, and maybe. The preferences of bed user will rule on this. Everyone has a different level of comfort and what he or she likes.  Generally, the response would be as follows:  the answer is yes for most people and most climates.  The answer is no for soft side waterbeds with a shallow fill. The answer is maybe for soft side waterbed with mid fill and very warm climates on other waterbeds.

The water in a waterbed takes on the temperature of the room.  In cold or cool climates, this means a cold or cool bed. Hardside waterbed heaters are inexpensive and will keep you comfortable. A warm bed helps improve your circulation and soothes sore and achy muscles while you sleep.  Many people sleep better and deeper in the warm comfort of a warm waterbed.

Waterbed heaters are inexpensive to buy for hardside beds.  These are more expensive to use, as the electrical consumption is higher.  An energy efficient model is available; the initial investment is higher but the monthly cost is less.  The heaters specially designed for the soft side bladders are more expensive due to the construction and low wattage requirements.  However, this heater is cheaper to run because it takes less electricity.

Soft side waterbeds are different due to their construction.  If you have a deep fill bladder, you will be sleeping on up to 8 inches of water, which could get cold.  If the mattress is on a wooden deck, you can use a regular waterbed heater up to 300 watts or you can buy a low wattage soft side waterbed heater designed for these beds.  This heater protects the bed from fires and is cheaper to use as it runs on 120 watts.

The mid fill bladders are usually about six inches deep and surrounded by thick foam.  If you want a heater, you must use the low watt heater.

A shallow fill contains very little water and needs no heat.

If you live in a very warm climate, you do not need a heater.

A waterbed heater is rather like an electric blanket.  It has a set of coils that are encased in plastic and lays under the waterbed mattress or bladder, as it is called. Many people prefer the temperatures to match their body temperature.

The cost of electrical usage is small in comparison to the value of a wonder night's sleep in the comfort of these special beds.