Most of the cost of a shower is not the water itself but the energy used to heat it, so anything that cuts how much hot water you use cuts the bill twice over. A low-flow or aerating showerhead does exactly that, often without the weak dribble people fear.
How they keep the feel without the flow
An aerating showerhead mixes air into the water, so the spray feels full and powerful while actually using less water. Other designs use cleverly shaped nozzles to maintain pressure at a lower flow. Either way the aim is the same, a satisfying shower from fewer litres a minute, which means less hot water drawn and less energy spent heating it. For many people the difference in feel is barely noticeable once fitted.
The double saving
Using less hot water saves on both the water bill, if you are metered, and the far larger energy cost of heating it. Across a household showering daily, trimming the flow rate adds up to a meaningful annual saving for the price of a showerhead. Combine it with keeping showers brisk, as the hot water page suggests, and the two together make a real dent without anyone feeling deprived.
Mind which shower you have
There is one important exception. Electric showers heat water on demand and already control their own flow, so a low-flow head offers little there and can occasionally upset them. The same caution applies to certain low-pressure gravity-fed systems, where restricting the flow further leaves a feeble trickle. Low-flow heads suit mains-pressure and combi-fed mixer showers best, so check what you have before buying.
Even cheaper options
If a new head is not worth it, a simple shower timer or even a favourite four-minute song nudges the habit in the right direction for nothing. Some water companies give aerators and flow regulators away free, so it is worth checking yours before paying. The principle holds either way: every litre of hot water you do not use is energy you do not pay to heat.