2 Feb 2006

On teenagers and showers

Our total household water consumption currently stands at 350m3 per annum. That’s just under 1000 litres per day. Bear in mind, if you didn’t already know it, that 1000 litres of water occupies a cubic metre of space and that water companies habitually sell water by the cubic metre rather than the litre, just to save three confusing noughts on the bill.

Now 350m3 per annum is a large figure, even for a family of five. Water company guidelines, used to set prices, suggest that a family of five should be averaging no more than 230m3 per annum and indeed, in our first few years in this house, first occupied in 1993, that’s more or less what we consumed. But as our three boys got older, the consumption level has crept up and up and their current predilection for showers has ratcheted up our water usage to new heights. We are consuming 50% more water than we ought to. Yikes! What is our excuse?

Well, m’lud, when they were babies, they made do with one shared bath a day. Now they all shower. This morning I timed Jack, our eldest, in and out of the shower. Discreetly, you understand. I don’t think he even knew I was clocking him but I was keeping an ear out. He took eight minutes. God knows what he does in the shower for eight minutes each day: it’s a long time since I was seventeen and I think we only had crap showers back in 1970 and so we used to soak in baths. Showers were seen as a way of saving water. Not any more.

Jack is the worst for long showers but the other two aren’t far behind. I reckon that, between us, our family of five probably account for around 20 minutes in the shower each day. Maybe even a little more. And each of our showers delivers 20 litres of water per minute and our water bills bear this out in black and white. I think the switch to using showers accounts for almost all this increase in our water consumption. A bath once a day uses maybe 100 litres. 20 minutes of showers at 20 litres per minute uses 400 litres. The difference, 300 litres, times 365 days a year is 109m3. And we’ve gone from 230m3 per annum to 350m3. Hmm.

The additional water cost? Cambridge Water Company are currently billing us £1.75 for each cubic meter of water (inc both supply and sewerage). So the extra 109m3 will be costing us £190 a year.

But what about the effect on our heating bills?

We use an oil-fired boiler and I log its consumption, just as I log the water bills. There isn’t quite such an obvious trend here for domestic hot water heating duties fall some way behind space-heating as far as the boiler is concerned. And, of course, space-heating demand varies from year to year. But nevertheless there is an appreciable upward trend to be observed. In the early days, the 1990s, we used just over 6 litres of heating oil per day, averaged throughout the year. But during the past two years (i.e. 2004 and 2005), our oil burn has crept up to 7 litres per day.

Now a litre of heating oil, costing 35p, contains just over 10kWh of energy. Because the boiler isn’t the most up-to-date condensing model, this only produces around 8kWh of energy in the hot water systems. This additional 8kWh is enough to heat up 140 litres of water from 8°C to 60°C.

Now, if we are using an extra 300 litres of water a day in the showers, around two thirds of this will need to be heated in order to get a nice shower temperature at around 43°C. So this would suggest the extra showers would consume 100 litres of cold water and 200 litres of hot water. 200 litres or 140 litres? The figures are a bit fuzzy, but there can be no doubt that our changing habits are showing through on both water and oil consumption.

The additional heating cost? 200 litres of extra hot water a day equates to an additional 14kWh energy used, after boiler inefficiencies are accounted for. That is 4,900kWh extra per annum, equivalent to 480 litres of heating oil, costing currently 35p per litre, or £168 each year.

Add this £168 to the water costs (£190), and you can see that the boys’ love of power showers is costing us £350 a year.


The most obvious point is that power showers are incredibly resource hungry. Whilst a huge amount of effort seems to have been spent on producing products like washing machines, and fridges which consume less water and less power, these savings pall into insignificance when set against the extra demand we are placing on our showers. There is Part L of the building regs banging on about fitting four compact fluorescent lightbulbs (annual saving around 300kWh) and using argon in double glazed sealed units (annual saving another 300kWh): meanwhile a household growing up and starting to use to power showers adds 4,900kWh to the annual energy consumption, more than the entire lighting load for the same household.

Having said that, this figure of 4,900kWh per annum is itself dwarfed by the energy used to fly a family of five to Spain and back. That’s around 25,000kWh, which is equivalent to the entire space heating and hot water requirements of our household for any given year.

It makes you realise just how anal our energy saving regulations have become. And how incredibly difficult it will be to bring about significant reductions in our energy consumption. Not to mention our water consumption. For every energy and water saving measure we introduce, we seem to find a new device which more than cancels out the benefits.

Having said that, there is obviously great scope to produce both energy savings and water savings from designing clever showers, which give the feel of a power shower from a greatly reduced flow rate.

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