We have just bought a venturi shower head for Yarwood.
The blurb says that...
"A conventional shower has a flow rate of 25 to 30 litres per minute so a five minute shower uses around 125 litres of water. The Venturi shower use only 6 or 8 litres per minute, so you save over 90 litres having a 5 minute shower, cutting water and energy consumption up to 70%."
The flow of water to the shower head is restricted but a 'vent' in the base of the shower head handle sucks in air which aerates the flow of water and increases the pressure again - result you feel satisfied with the flow and shower experience but have used less water.
Now that has got to worth a try ..