Just got a water bill for our new home. We’ve been here 2 months. Yorkshire Water have estimated our water usage at 0 units. Twats.
I have just read the meter and we have used 6 units. That’s 6 m3 in 60 (ish) days. Or about 100 litres a day. Two of us live here, so that’s 50 litres each per day. Yay for us (the UK average is about 150 litres per person per day).
Our new house has an annoying on-demand boiler which means we often run cold water straight down the drain when doing the washing up; our old house stored hot water in a cylinder. The only time I bothered to do the calculation at our old house I came up with 90 litres (between us, so 45 each) per day. The waste of water annoys me, but from the numbers it’s clearly not a huge waste of water. So that’s good. And I’m sure we burn less gas with the on-demand boiler.
The number of units of water used is so small that to do it properly I should use a year’s worth of bills. That would also eliminate the seasonal variation. I’m pretty sure we use more water in summer: We don’t water the garden (we don’t have one, but we didn’t when we did have one anyway), but we do water the tomatoes, chilis, and courgettes, or whatever we’re growing (still, this probably only amounts to a few litres per day). We also wash the car, not often, but I’m sure we wash it more in summer than winter, just because it’s warmer and nicer to be outside washing the car. We have just replaced our car with something a lot newer (with emissions of 119 g/Km CO2, yay!), so perhaps we’ll be washing the car more often. Perhaps we drink more in the summer too.
When we moved in I had to find out where our water meter was. There are 4 water meters outside on the street in a cluster, but Yorkshire Water helpfully told us which one it was (they had a note on file, saving me from struggling to read the serial number). To check, I got my partner to turn on the tap whilst I watched the meter. The meter actually measures down to the litre (in red digits that don’t go on the bill), and has another spinny thing that probably does 10 revs per liter, so this is a totally feasible exercise. I recommend that everyone try this, watching that meter spin round furiously just from turning on the tap was quite frightening.
I note that my bill is in m3 but all the discussion about water consumption is in litres (average consumption is 150 litres, bath and kettle sizes are quoted in litres). This is okay, everyone knows that there are 1000 litres in a m3, right? Apparently not. I asked two people I know that I consider intelligent and fairly numerate, as well as occasionally taking an interest in these things; they both have degrees, and not in underwater needlework. Neither of them knew the answer straight away to how many litres were in a m3. Both, when prodded, remembered that a litre is equivalent to a cube 10cm x 10cm x 10cm; one immediately realised that this meant there must be 1000 litres per m3, the other had to be prodded again. I conclude that the quality of maths teaching in this country is appalling.
I also conclude that it would be more helpful to have water bills that say 1000 litres instead of m3. Because then it would be easier for consumers to relate their bill to their baths. Should we use kl? Dunno, always makes me laugh a bit, for some reason.
code monk 
2009-01-15 at 18:01:03
We have one of those instant-on flash heaters to supplement our solar hot water heating system. One of the nice features that we added when we spec’d out the system was a recirculation pump. In order to use this, we had to run some additional pipe to return the water in the hot water line back to the intake of the heater.
When we want hot water, we push a button. The pump circulates the cold water from the hot water line back through the system, and stops running when the temperature sensor detects that the recirculated water is hot. The runs for our hot water are fairly short, so I don’t think we lose very much energy from this. What’s nice is that we never have to run water down the drain waiting for it to heat up.
My guess is that your concern here is largely academic, given that you don’t live in a desert, but if you care deeply about the water you’re dumping, there is a solution… :’)
2009-01-16 at 08:14:27
I like this idea, and I hadn’t come across it before.
I’m not sure where you think energy might be lost. Given that the alternative to recirculating the warming water is flushing it, surely any heat that is recirculated is a gain, compared to flushing it? Running the pump to recirculate the water uses energy, but probably not much.
I wonder if it meets UK building code.
2009-01-16 at 18:29:15
The energy that’s lost is lost when you stop using the water and the water dissipates its heat into the walls (or floor) of your house through the pipes. Admittedly you lose this same energy if you don’t have the pump, so it’s not a disadvantage of the pump. In winter it’s really not a loss at all because it’s heating your living space, but in summer it can be a double loss if you use air conditioning.
I guess you could come up with a system for flushing the hot water into a holding tank so as not to lose its heat, but it probably wouldn’t pay for itself. I’m just enough of a pedant that I tend to worry about such things anyway… :’)