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I had always assumed that showers (excluding power showers) used less water than baths until we were faced with a sudden large increase in water use and heating costs. The increase came about due to one of our daughters living at home for a few months using a shower daily that was normally only used infrequently. As I was unwilling to carry on absorbing the increased costs I decided to investigate further and the results were to say the least enlightening.
I measured the flow rate of the shower concerned and discovered it was 11 litres/minute, so a ten minute shower used 110 litres of water. The water pressure was 2.1 bar for both hot and cold water (we have a hot water system that runs at mains pressure). A normal sized bath holds around 70 litres plus a person. This started to explain the high water use and the lack of hot water. A bit of research on the internet indicated the lowest acceptable flow rate was around 4 litres a minute and that there are three ways to control the shower water flow - the choice of shower head, using a flow restrictor and adjustment of the mixer valve (not all types).
It also became apparent during this research that there a number of pitfalls to avoid when making changes. So called 'Eco' shower heads are not suitable for power showers, gravity fed systems where the pressure is less than 0.5 bar and some combi boilers, in addition they can vibrate with pressures above 2 bar meaning a flow restrictor is also required. Eco shower heads work by mixing air with the water and do give a reduced flow, they tend to be more expensive. The same reduction in flow can be achieved in other ways but the quality of the shower is degraded. As part of this exercise I purchased one made by Mira for £34.
Further investigation also revealed a simpler method of reducing water use in the shower which will work for some people - turn the water off during the shower when you don't need it.
Measured Results
The measured results for our two showers are shown below:
| Shower |
Setting |
Flow Rate |
| Shower 1 with original shower head |
n-a |
11 litres/min |
| Shower 1 with Eco Shower Head & Flow Restrictor |
1 |
6.5 litres/min |
| Shower 1 with Eco Shower Head & Flow Restrictor |
2 |
6 litres/min |
| Shower 1 with Eco Shower Head & Flow Restrictor |
3 |
5.5 litres/min |
| Shower 2 (flow rate limited by mixer) |
n-a |
5 litres/min |
Payback Time
The measured water saving is around 5 litres/minute and water costs are around £2.10 per cubic metre (excluding fixed costs). Shower head cost is £34 so this represents 16.2 cubic meters of water. 16.2 cubic metres divided by 5 litres is equivalent to 3240 minutes of use. Assuming 10 minutes use per day for one person the shower head will pay for itself in 324 days (just under a year) which is a good investment. If there are more people using the shower the payback time comes down proportionately and the investment looks even more attractive. These figures do not take into account the significant savings in water heating costs.
Measuring Shower Flow Rate
This is a very simple task requiring a bucket or bowl and a measuring jug. Run the shower into the bucket for one minute and then using the measuring jug measure how much water is in the bucket. The flow rate is the number of litres in the bucket per minute.
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