A conventional shower is just a means of mixing hot and cold water, and spraying it at you. It is simple and cheap, but its performance is highly dependent on the water supplies to it.

If upstairs in a house with a conventional cistern-fed hot water supply, there will be very little pressure, and hence the shower may be very poor. By reducing the restriction of the shower head as much as possible, you may be able to get quite a lot of water pouring out from the large reservoir of the cistern, but with little force. This is an example of low pressure, but high flow rate. There may also be temperature fluctuations caused by water being drawn off elsewhere, and a thermostatic valve can be used to compensate for this.

If the hot water is at high pressure, such as from a combination boiler (q.v.) or multipoint or a Megaflo (q.v.), then the shower will be better, but may still be limited by the resistance of the incoming rising main. A thermostatic valve is recommended for combi boilers, because they sometimes produce rapid fluctuations in water temperature.

Conventional showers must be fed with hot and cold water of the same pressure, with the exception of a special valve which uses low pressure hot and high pressure cold. This also claims to boost the flow rate of the hot water by taking advantage of the pressure of the cold water.