The thermostatic shower is a popular device utilizing a memory allowing you to maintain the desired temperature of the shower, even between uses. Thermostatic showers are mechanized in order to give the user better control over how the shower behaves. The purpose of the thermostatic shower is to allow the shower user to set the heat at which they prefer their shower. Water temperature is held constant in the event water is being used in other parts of the home.
Manual showers, much more traditional and more common, simply use water from the hot water tank, without any control of the temperature beyond the preset temperature on the water heater.
Thermostatic showers are more reliable than manual showers, although there can be some problems in regulating the water flow.
Thermostatic showers work by regulating the flow of water into the shower head, so that the water stays at a constant temperature, rather than being affected by water being used in other parts of the house, which can sometimes affect the amount of hot water which travels to the shower.
Users of thermostatic showers are sometimes concerned that the way in which the water is controlled will effect the amount of water which is pushed through the shower head. However, the technology which allows the thermostatic shower to maintain the temperature of the water should not prevent flow rates. Flow rates should remain constant, as the thermostatic shower is designed to control the temperature and rate of the water. The temperature of water therefore ought not to be affected by the running of water in different parts of the house, although this is the well-known bane of many shower-user's life.
Water flow rates to the shower head may be affected by the amount of hot and cold water being used by the heating system, but the water flow of the shower itself should not change. The other problem with the water flow rates of a thermostatic shower is the availability of the water that the shower is remembering: a certain temperature may require less water than another, and so flow rates can also be affected in this manner, but it should be very minor.
A manual shower is much more dependent upon the flowing of water in other parts of the house. With a manual shower, there is no control of the water, and so flow rates are not consistent. This does not mean that more sophisticated manual showers, such as the power-shower, cannot control the flow of water somewhat, but it will be less consistent than with the thermostatic shower, and the temperature will also not be controlled by the shower.
Water flow which is controlled by the type of shower being used should be constant, but in manual showers which do not have this capacity, the water flow can be affected by problems with the receipt of water into the system.